Auto merge of #14039 - metajack:windows-wpt, r=jgraham

Fix test-wpt and test-css for Windows.

<!-- Please describe your changes on the following line: -->
In addition to minor changes for Windows, this forces Windows Python to
be used for all Windows builds (instead of using Windows Python only for
pc-windows-msvc builds).

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because testing the tests is too meta for me

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tests/wpt/run.py

@@ -49,7 +49,10 @@ def set_defaults(paths, kwargs):
 
     if kwargs["binary"] is None:
         bin_dir = "release" if kwargs["release"] else "debug"
-        bin_path = servo_path("target", bin_dir, "servo")
+        bin_name = "servo"
+        if sys.platform == "win32":
+            bin_name += ".exe"
+        bin_path = servo_path("target", bin_dir, bin_name)
 
         kwargs["binary"] = bin_path
 

tests/wpt/web-platform-tests/tools/sslutils/openssl.py

@@ -57,7 +57,13 @@ class OpenSSL(object):
             self.cmd += ["-config", self.conf_path]
         self.cmd += list(args)
 
-        env = os.environ.copy()
+        # Copy the environment, converting to plain strings. Windows
+        # StartProcess is picky about all the keys/values being plain strings,
+        # but at least in MSYS shells, the os.environ dictionary can be mixed.
+        env = {}
+        for k, v in os.environ.iteritems():
+            env[k.encode("utf8")] = v.encode("utf8")
+
         if self.base_conf_path is not None:
             env["OPENSSL_CONF"] = self.base_conf_path.encode("utf8")