The gold linker should not be used on Windows

[UK992]

After #9449 building on Windows failed:

$ ./mach build -r
Could not execute process `C:/msys64/home/Urban/servo/etc/rustc-with-gold -vV` (never executed)

Caused by:
  %1 is not a valid Win32 application. (os error 193)
Build completed in 0.14s

[jdm]

@larsbergstrom This seems difficult to get right!

[larsbergstrom]

@jdm Agreed :-)

Though a large part of it is also that we don't have CI up yet for all of our platforms. While I can say I should certainly know better, as we expand our platform matrix, it's pretty unreasonable to expect every reviewer to know the impact of small python changes on, say, the AARCH64 cross-build.

[larsbergstrom]

The change required here is that the python code that chooses to use the gold linker:

servo/python/servo/command_base.py

Line 382 in 220ead1

if self.config["tools"]["rustc-with-gold"]:

Should not do so if the sys.platform == 'win32'.

[UK992]

@larsbergstrom in MINGW64 shell, sys.platform return 'msys', not 'win32'.

[jasonwilliams]

So would we check both msys and win32?
In the long term it would be good not to be relying so heavily on the mingw64 stuff at all