servo: Merge #12377 - Build geckolib with MozillaBuild on Windows (from upsuper:build-with-mozillabuild); r=metajack

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Given #12319 removes the direct dependency of geckolib to gcc, geckolib is now compilable without gcc, and thus builds within MozillaBuild.

This changeset also changes the triple to use the MSVC backend rather than GNU for Windows . I'm not sure whether this change is necessary, but given we use MSVC to compile Gecko on Windows, I think we would eventually need this anyway. Triples for MinGW64 and Cygwin are unchanged, so that existing build targets should not be broken.

Servo itself is still not buildable with MozillaBuild. To make that work, some changes to mozjs are necessary as well.

It is probably worth some infra coverage to avoid regression.

---
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- [x] `./mach build -d` does not report any errors (on MinGW)
- [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 it only changes build system

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r? @bholley

Source-Repo: https://github.com/servo/servo
Source-Revision: 184b1ba91b5e73d4bbeacc9093f31f4c8570c0f4

servo/python/servo/build_commands.py

@@ -332,7 +332,7 @@ class MachCommands(CommandBase):
             opts += ["--release"]
 
         env = self.build_env()
-        env["CARGO_TARGET_DIR"] = path.join(self.context.topdir, "target", "geckolib")
+        env["CARGO_TARGET_DIR"] = path.join(self.context.topdir, "target", "geckolib").encode("UTF-8")
 
         build_start = time()
         with cd(path.join("ports", "geckolib")):

servo/python/servo/command_base.py

@@ -41,7 +41,9 @@ def host_triple():
         os_type = "apple-darwin"
     elif os_type == "android":
         os_type = "linux-androideabi"
-    elif os_type == "windows" or os_type.startswith("mingw64_nt-") or os_type.startswith("cygwin_nt-"):
+    elif os_type == "windows":
+        os_type = "pc-windows-msvc"
+    elif os_type.startswith("mingw64_nt-") or os_type.startswith("cygwin_nt-"):
         os_type = "pc-windows-gnu"
     elif os_type == "freebsd":
         os_type = "unknown-freebsd"