[Windows] Don't try to use x64 linker on ARM64 Windows.

Trying to invoke an x64 binary on ARM64 Windows 10 won't work, and will
print an obscure error message.  Choose the 32-bit linker instead, which
will run under emulation.

The x64 linker should in theory run under ARM64 Windows 11.  We could
detect this using IsWow64GuestMachineSupported(), but I don't have a
setup to test that with at the moment.

Differential Revision: https://reviews.llvm.org/D120681