Cross compilation to Windows broken

[Jake-Shadle]

PR #57 broke cross compilation to Windows since it returned to the behavior that assumes that the MSVC toolchain, in particular ml64, is available and can be used.

I can submit a fix for this, would it be ok to add a CI step that tests that cross compilation from Linux works and that the tests run under wine?

[nagisa]

Sorry, ml is required for i686-pc-windows-msvc to work at all. This is a much more important use-case I feel and the cross-compilation functionality was breaking rustc (rust-lang/rust#87680). Hence the regression.

Since we have a test for what rustc needs now, I'm happy to accept improvements that add cross-compilation support again in a way that does not break the rustc use-case.