Define WIN32_LEAN_AND_MEAN before including windows.h.
Don't assert in Interlocked.Add () icalls on 64-bit systems.

The checks here were wrong in the first place; they should have
checked for MONO_ARCH_HAVE_ATOMIC_ADD rather than SIZEOF_VOID_P.
But regardless, these methods need to work when invoked via
reflection, which they wouldn't previously.
Ignore .dirstamp files.
Add a .gitignore file to support/minizip/ to ignore *.la *.lo files.
Silence some noisy warnings in mono/tests/.
Enum subtraction quirk needs to work with numeric constants only. Fixes #15520