Auto merge of #24004 - servo:win-gstreamer, r=ferjm

Enable GStreamer on Windows.

I have verified that desktop and emulator UWP builds work with this set of DLLs.

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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because no tests for UWP

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python/servo/build_commands.py

@@ -270,6 +270,8 @@ class MachCommands(CommandBase):
                 print("Can't find Visual C++ %s installation at %s." % (vs_version, vcinstalldir))
                 sys.exit(1)
 
+            env['PKG_CONFIG_ALLOW_CROSS'] = "1"
+
         if uwp:
             # Don't try and build a desktop port.
             libsimpleservo = True