ci: Add a job for testing win32 with no extra stack alignment, like msvc

This test builds with clang, as GCC defaults to 16 byte stack alignment on windows, while clang defaults to 4.

This adds an undocumented meson option for overriding stack alignment.

@gramner Does this look sensible and useful to you? Do you want to give it a try with modifying some asm to break if it assumes too much stack alignment?