Auto merge of #23211 - jdm:win-cross, r=SimonSapin

Add Windows x86 build job.

This will make it easier to start working on Hololens embedding work without having to deal with a broken build first.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes

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---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/23211)
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Cargo.lock

@@ -148,7 +148,7 @@ name = "azure"
 version = "0.35.0"
 source = "git+https://github.com/servo/rust-azure#5c648f2bd5d2d600c28d56f07c29c4e2a08173b6"
 dependencies = [
- "cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cmake 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.19.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
  "servo-freetype-sys 4.0.4 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -191,7 +191,7 @@ name = "backtrace-sys"
 version = "0.1.24"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -427,7 +427,7 @@ name = "bzip2-sys"
 version = "0.1.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -500,7 +500,7 @@ dependencies = [
 
 [[package]]
 name = "cc"
-version = "1.0.18"
+version = "1.0.35"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 
 [[package]]
@@ -594,10 +594,10 @@ dependencies = [
 
 [[package]]
 name = "cmake"
-version = "0.1.29"
+version = "0.1.38"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -1190,7 +1190,7 @@ name = "energymon-builder"
 version = "0.3.0"
 source = "git+https://github.com/energymon/energymon-sys.git#f8d77ea2906b25f9c0fd358aa9d300a46dc3e97c"
 dependencies = [
- "cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cmake 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)",
  "pkg-config 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1275,7 +1275,7 @@ name = "expat-sys"
 version = "2.1.6"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cmake 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)",
  "pkg-config 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -1325,7 +1325,7 @@ name = "fontsan"
 version = "0.4.0"
 source = "git+https://github.com/servo/fontsan#29e879c870348c4b3fd51086e42dbb6365171479"
 dependencies = [
- "cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cmake 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
  "miniz-sys 0.1.10 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -1869,7 +1869,7 @@ name = "harfbuzz-sys"
 version = "0.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cmake 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)",
  "freetype 0.4.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "pkg-config 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -1940,7 +1940,7 @@ name = "heartbeats-simple-sys"
 version = "0.4.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cmake 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
  "pkg-config 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
@@ -2175,7 +2175,7 @@ name = "jemalloc-sys"
 version = "0.1.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -2429,7 +2429,7 @@ name = "libloading"
 version = "0.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -2494,10 +2494,10 @@ dependencies = [
 
 [[package]]
 name = "libz-sys"
-version = "1.0.18"
+version = "1.0.25"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
  "pkg-config 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "vcpkg 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2713,7 +2713,7 @@ name = "miniz-sys"
 version = "0.1.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -2731,7 +2731,7 @@ name = "miniz_oxide_c_api"
 version = "0.1.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "crc 1.8.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
  "miniz_oxide 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2797,7 +2797,7 @@ name = "mozangle"
 version = "0.1.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -2806,7 +2806,7 @@ name = "mozjs"
 version = "0.10.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "lazy_static 1.2.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -2820,9 +2820,9 @@ version = "0.61.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "bindgen 0.49.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
- "libz-sys 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "libz-sys 1.0.25 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -2959,7 +2959,7 @@ version = "0.11.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "bitflags 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "cfg-if 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
  "void 1.0.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3097,7 +3097,7 @@ name = "openssl-sys"
 version = "0.9.35"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
  "pkg-config 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
  "vcpkg 0.2.2 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3462,7 +3462,7 @@ dependencies = [
 
 [[package]]
 name = "rust-webvr"
-version = "0.10.3"
+version = "0.10.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "bindgen 0.49.0 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3557,7 +3557,7 @@ dependencies = [
  "canvas_traits 0.0.1",
  "caseless 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "chrono 0.4.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cmake 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)",
  "cookie 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "crossbeam-channel 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "cssparser 0.25.5 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3802,7 +3802,7 @@ version = "0.0.1"
 dependencies = [
  "backtrace 0.3.9 (registry+https://github.com/rust-lang/crates.io-index)",
  "bitflags 1.0.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "crossbeam-channel 0.3.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.19.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "gleam 0.6.13 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3815,7 +3815,7 @@ dependencies = [
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "osmesa-src 0.1.0 (git+https://github.com/servo/osmesa-src)",
  "osmesa-sys 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
- "rust-webvr 0.10.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rust-webvr 0.10.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "sig 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "tinyfiledialogs 3.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "winapi 0.3.6 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -3855,7 +3855,7 @@ name = "servo-freetype-sys"
 version = "4.0.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cmake 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)",
  "pkg-config 0.3.14 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -3993,7 +3993,7 @@ version = "0.30000020.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
  "cgl 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
- "cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cmake 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)",
  "euclid 0.19.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "expat-sys 2.1.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "gleam 0.6.13 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -4203,7 +4203,7 @@ version = "0.0.1"
 dependencies = [
  "android_injected_glue 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)",
  "android_logger 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "jni 0.10.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -4462,7 +4462,7 @@ dependencies = [
 name = "task_info"
 version = "0.0.1"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
 [[package]]
@@ -4572,7 +4572,7 @@ name = "tinyfiledialogs"
 version = "3.3.5"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 dependencies = [
- "cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)",
+ "cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)",
  "libc 0.2.44 (registry+https://github.com/rust-lang/crates.io-index)",
 ]
 
@@ -5142,7 +5142,7 @@ dependencies = [
  "ipc-channel 0.11.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
  "msg 0.0.1",
- "rust-webvr 0.10.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rust-webvr 0.10.4 (registry+https://github.com/rust-lang/crates.io-index)",
  "script_traits 0.0.1",
  "servo_config 0.0.1",
  "webvr_traits 0.0.1",
@@ -5405,7 +5405,7 @@ dependencies = [
 "checksum bzip2-sys 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)" = "6584aa36f5ad4c9247f5323b0a42f37802b37a836f0ad87084d7a33961abe25f"
 "checksum caseless 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "808dab3318747be122cb31d36de18d4d1c81277a76f8332a02b81a3d73463d7f"
 "checksum cbindgen 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0ae5776bf2f6d5ff4f07eb63aa666fd9e1dbe0fe4b87f0fa32b469efae2940f7"
-"checksum cc 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)" = "2119ea4867bd2b8ed3aecab467709720b2d55b1bcfe09f772fd68066eaf15275"
+"checksum cc 1.0.35 (registry+https://github.com/rust-lang/crates.io-index)" = "5e5f3fee5eeb60324c2781f1e41286bdee933850fff9b3c672587fed5ec58c83"
 "checksum cesu8 1.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "6d43a04d8753f35258c91f8ec639f792891f748a1edbd759cf1dcea3382ad83c"
 "checksum cexpr 0.3.3 (registry+https://github.com/rust-lang/crates.io-index)" = "8fc0086be9ca82f7fc89fc873435531cb898b86e850005850de1f820e2db6e9b"
 "checksum cfg-if 0.1.6 (registry+https://github.com/rust-lang/crates.io-index)" = "082bb9b28e00d3c9d39cc03e64ce4cea0f1bb9b3fde493f0cbc008472d22bdf4"
@@ -5416,7 +5416,7 @@ dependencies = [
 "checksum clipboard 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)" = "25a904646c0340239dcf7c51677b33928bf24fdf424b79a57909c0109075b2e7"
 "checksum clipboard-win 2.1.1 (registry+https://github.com/rust-lang/crates.io-index)" = "14cc3e6c075926b96490d5f90d4a5af7be8012a4d8a8698e619655085a7641a3"
 "checksum cloudabi 0.0.3 (registry+https://github.com/rust-lang/crates.io-index)" = "ddfc5b9aa5d4507acaf872de71051dfd0e309860e88966e1051e462a077aac4f"
-"checksum cmake 0.1.29 (registry+https://github.com/rust-lang/crates.io-index)" = "56d741ea7a69e577f6d06b36b7dff4738f680593dc27a701ffa8506b73ce28bb"
+"checksum cmake 0.1.38 (registry+https://github.com/rust-lang/crates.io-index)" = "96210eec534fc3fbfc0452a63769424eaa80205fda6cea98e5b61cb3d97bcec8"
 "checksum cocoa 0.18.4 (registry+https://github.com/rust-lang/crates.io-index)" = "cf79daa4e11e5def06e55306aa3601b87de6b5149671529318da048f67cdd77b"
 "checksum color_quant 1.0.0 (registry+https://github.com/rust-lang/crates.io-index)" = "a475fc4af42d83d28adf72968d9bcfaf035a1a9381642d8e85d8a04957767b0d"
 "checksum combine 3.5.2 (registry+https://github.com/rust-lang/crates.io-index)" = "54cedd8056314afe0d844a37a207007edf8a45f2cc452fd77629cd63c221740e"
@@ -5565,7 +5565,7 @@ dependencies = [
 "checksum libdbus-sys 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "99c78106156a964aadc1c59f7798276967be6705243b60f3ab7e131e3841db88"
 "checksum libflate 0.1.19 (registry+https://github.com/rust-lang/crates.io-index)" = "bff3ac7d6f23730d3b533c35ed75eef638167634476a499feef16c428d74b57b"
 "checksum libloading 0.5.0 (registry+https://github.com/rust-lang/crates.io-index)" = "9c3ad660d7cb8c5822cd83d10897b0f1f1526792737a179e73896152f85b88c2"
-"checksum libz-sys 1.0.18 (registry+https://github.com/rust-lang/crates.io-index)" = "87f737ad6cc6fd6eefe3d9dc5412f1573865bded441300904d2f42269e140f16"
+"checksum libz-sys 1.0.25 (registry+https://github.com/rust-lang/crates.io-index)" = "2eb5e43362e38e2bca2fd5f5134c4d4564a23a5c28e9b95411652021a8675ebe"
 "checksum line_drawing 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)" = "5cc7ad3d82c845bdb5dde34ffdcc7a5fb4d2996e1e1ee0f19c33bc80e15196b9"
 "checksum linked-hash-map 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "70fb39025bc7cdd76305867c4eccf2f2dcf6e9a57f5b21a93e1c2d86cd03ec9e"
 "checksum linked_hash_set 0.1.3 (registry+https://github.com/rust-lang/crates.io-index)" = "3c7c91c4c7bbeb4f2f7c4e5be11e6a05bd6830bc37249c47ce1ad86ad453ff9c"
@@ -5652,7 +5652,7 @@ dependencies = [
 "checksum regex-syntax 0.6.3 (registry+https://github.com/rust-lang/crates.io-index)" = "fbc557aac2b708fe84121caf261346cc2eed71978024337e42eb46b8a252ac6e"
 "checksum remove_dir_all 0.5.1 (registry+https://github.com/rust-lang/crates.io-index)" = "3488ba1b9a2084d38645c4c08276a1752dcbf2c7130d74f1569681ad5d2799c5"
 "checksum ron 0.1.7 (registry+https://github.com/rust-lang/crates.io-index)" = "da06feaa07f69125ab9ddc769b11de29090122170b402547f64b86fe16ebc399"
-"checksum rust-webvr 0.10.3 (registry+https://github.com/rust-lang/crates.io-index)" = "a59e731de33df7fca446711d7cf31552a1c550db5da3310588579d1124f4d00b"
+"checksum rust-webvr 0.10.4 (registry+https://github.com/rust-lang/crates.io-index)" = "dd268264db4808e78ad1738ce1ff10a8bd53fb5ba408f595763174ca4a6fb875"
 "checksum rust-webvr-api 0.10.4 (registry+https://github.com/rust-lang/crates.io-index)" = "1b2af5c6c86fb79e70b5a34daa3d488411225707c73dc5467c7da7c83d557daf"
 "checksum rustc-demangle 0.1.4 (registry+https://github.com/rust-lang/crates.io-index)" = "3058a43ada2c2d0b92b3ae38007a2d0fa5e9db971be260e0171408a4ff471c95"
 "checksum rustc_version 0.2.3 (registry+https://github.com/rust-lang/crates.io-index)" = "138e3e0acb6c9fb258b19b67cb8abd63c00679d2851805ea151465464fe9030a"

components/script/build.rs

@@ -9,11 +9,47 @@ use std::fmt;
 use std::fs::File;
 use std::io::Write;
 use std::path::PathBuf;
+use std::process::Command;
+use std::str;
 use std::time::Instant;
 
 fn main() {
     let start = Instant::now();
 
+    let target = env::var("TARGET").unwrap();
+    let host = env::var("HOST").unwrap();
+    if target.contains("windows") && host != target {
+        assert_eq!(
+            host, "x86_64-pc-windows-msvc",
+            "Only cross-compiling from x64 is supported"
+        );
+        assert_eq!(
+            target, "i686-pc-windows-msvc",
+            "Only cross-compiling to x86 is supported"
+        );
+        assert!(env::var("VSINSTALLDIR").is_err());
+        // When cross-compiling on Windows, we need to ensure that the PATH is
+        // set up appropriately for the target before invoking make.
+        if env::var("VCVARSALL_PATH").is_err() {
+            panic!(
+                "Need to provide VCVARSALL_PATH value with path to \
+                 vcvarsall.bat from Visual Studio installation"
+            );
+        }
+
+        let vcvars = Command::new("vcvars.bat").output().unwrap();
+        assert!(vcvars.status.success());
+        let output = str::from_utf8(&vcvars.stdout).unwrap();
+        for line in output.lines() {
+            let mut parts = line.splitn(2, '=');
+            if let Some(name) = parts.next() {
+                if let Some(value) = parts.next() {
+                    env::set_var(name, value);
+                }
+            }
+        }
+    }
+
     // This must use the Ninja generator -- it's the only one that
     // parallelizes cmake's output properly.  (Cmake generates
     // separate makefiles, each of which try to build

components/script/vcvars.bat

@@ -0,0 +1,2 @@
+call "%VCVARSALL_PATH%\vcvarsall.bat" x64_x86
+set

etc/taskcluster/decision_task.py

@@ -32,6 +32,7 @@ def main(task_for):
         all_tests = [
             linux_tidy_unit_docs,
             windows_unit,
+            windows_x86,
             macos_unit,
             magicleap_dev,
             android_arm32_dev,
@@ -57,7 +58,7 @@ def main(task_for):
 
             "try-mac": [macos_unit],
             "try-linux": [linux_tidy_unit_docs],
-            "try-windows": [windows_unit],
+            "try-windows": [windows_unit, windows_x86],
             "try-magicleap": [magicleap_dev],
             "try-arm": [linux_arm32_dev, linux_arm64_dev],
             "try-wpt": [linux_wpt],
@@ -120,9 +121,16 @@ linux_build_env = {
 }
 macos_build_env = {}
 windows_build_env = {
+    "x86": {
+        "LIB": "%HOMEDRIVE%%HOMEPATH%\\gst\\gstreamer\\1.0\\x86\\lib;%LIB%",
+        "GSTREAMER_1_0_ROOT_X86": "%HOMEDRIVE%%HOMEPATH%\\gst\\gstreamer\\1.0\\x86\\",
+    },
+    "x86_64": {
         "LIB": "%HOMEDRIVE%%HOMEPATH%\\gst\\gstreamer\\1.0\\x86_64\\lib;%LIB%",
         "GSTREAMER_1_0_ROOT_X86_64": "%HOMEDRIVE%%HOMEPATH%\\gst\\gstreamer\\1.0\\x86_64\\",
+    },
 }
+
 windows_sparse_checkout = [
     "/*",
     "!/tests/wpt/metadata",
@@ -301,6 +309,20 @@ def android_x86_wpt():
     )
 
 
+def windows_x86():
+    return (
+        windows_build_task("Dev build", package=False, arch="x86")
+        .with_treeherder("Windows x86")
+        .with_env(**{
+            "VCVARSALL_PATH": "C:\\Program Files (x86)\\Microsoft Visual Studio\\2017\\BuildTools\\VC\\Auxiliary\\Build"
+        })
+        .with_script(
+            "python mach build --dev --target i686-pc-windows-msvc",
+        )
+        .find_or_create("build.windows_x86_dev." + CONFIG.git_sha)
+    )
+
+
 def windows_unit():
     return (
         windows_build_task("Dev build + unit tests")
@@ -556,26 +578,41 @@ def android_build_task(name):
     )
 
 
-def windows_build_task(name):
+def windows_build_task(name, package=True, arch="x86_64"):
-    return (
+    hashes = {
+        "devel": {
+            "x86_64": "b13ea68c1365098c66871f0acab7fd3daa2f2795b5e893fcbb5cd7253f2c08fa",
+            "x86": "50a18d050cdbb0779cd00607cc00a90f24fac48f2fb6c622ade6f23f050feb7a",
+        },
+        "non-devel": {
+            "x86_64": "f4f20c713766ed6718b914b9ae57ed993a59ffe194e6ef530c8547508b4484d8",
+            "x86": "52692c12ba8c3f59b5a289050e146d34d8374ab32b9f5070f7d1e37809656068",
+        },
+    }
+    version = "1.14.3"
+    task = (
         windows_task(name)
         .with_max_run_time_minutes(60)
-        .with_env(**build_env, **windows_build_env)
+        .with_env(**build_env, **windows_build_env[arch])
         .with_repo(sparse_checkout=windows_sparse_checkout)
         .with_python2()
         .with_rustup()
         .with_repacked_msi(
-            url="https://gstreamer.freedesktop.org/data/pkg/windows/" +
+            url=("https://gstreamer.freedesktop.org/data/pkg/windows/" +
-                "1.14.3/gstreamer-1.0-x86_64-1.14.3.msi",
+                 "%s/gstreamer-1.0-%s-%s.msi" % (version, arch, version)),
-            sha256="f4f20c713766ed6718b914b9ae57ed993a59ffe194e6ef530c8547508b4484d8",
+            sha256=hashes["non-devel"][arch],
             path="gst",
         )
         .with_repacked_msi(
-            url="https://gstreamer.freedesktop.org/data/pkg/windows/" +
+            url=("https://gstreamer.freedesktop.org/data/pkg/windows/" +
-                "1.14.3/gstreamer-1.0-devel-x86_64-1.14.3.msi",
+                 "%s/gstreamer-1.0-devel-%s-%s.msi" % (version, arch, version)),
-            sha256="b13ea68c1365098c66871f0acab7fd3daa2f2795b5e893fcbb5cd7253f2c08fa",
+            sha256=hashes["devel"][arch],
             path="gst",
         )
+    )
+    if package:
+        task = (
+            task
             .with_directory_mount(
                 "https://github.com/wixtoolset/wix3/releases/download/wix3111rtm/wix311-binaries.zip",
                 sha256="37f0a533b0978a454efb5dc3bd3598becf9660aaf4287e55bf68ca6b527d051d",
@@ -583,6 +620,7 @@ def windows_build_task(name):
             )
             .with_path_from_homedir("wix")
         )
+    return task
 
 
 def macos_build_task(name):

etc/taskcluster/decisionlib.py

@@ -476,8 +476,8 @@ class WindowsGenericWorkerTask(GenericWorkerTask):
         ) \
         .with_file_mount(
             "https://static.rust-lang.org/rustup/archive/" +
-                "1.13.0/i686-pc-windows-gnu/rustup-init.exe",
+                "1.17.0/x86_64-pc-windows-msvc/rustup-init.exe",
-            sha256="43072fbe6b38ab38cd872fa51a33ebd781f83a2d5e83013857fab31fc06e4bf0",
+            sha256="002127adeaaee6ef8d82711b5c2881a1db873262f63aea60cee9632f207e8f29",
         )
 
     def with_repacked_msi(self, url, sha256, path):