Auto merge of #27619 - servo:rustup, r=jdm

Upgrade to rustc 1.48.0-nightly (623fb90b5 2020-09-26)

https://github.com/rust-lang/hashbrown/pull/159 reduced `size_of::<HashMap>()`

python/servo/command_base.py

@@ -1028,7 +1028,12 @@ install them, let us know by filing a bug!")
 
     def ensure_rustup_version(self):
         try:
-            version_line = subprocess.check_output(["rustup" + BIN_SUFFIX, "--version"])
+            version_line = subprocess.check_output(
+                ["rustup" + BIN_SUFFIX, "--version"],
+                # Silence "info: This is the version for the rustup toolchain manager,
+                # not the rustc compiler."
+                stderr=open(os.devnull, "wb")
+            )
         except OSError as e:
             if e.errno == NO_SUCH_FILE_OR_DIRECTORY:
                 print("It looks like rustup is not installed. See instructions at "

python/servo/packages.py

@@ -11,5 +11,5 @@ WINDOWS_MSVC = {
     "openssl": "111.3.0+1.1.1c-vs2017-2019-09-18",
     "gstreamer-uwp": "1.16.0.5",
     "openxr-loader-uwp": "1.0",
-    "xargo": "v0.3.17",
+    "xargo": "v0.3.22",
 }