gh-79218: Define `MS_WIN64` macro for Mingw-w64 64bit on Windows by GalaxySnail · Pull Request #100137 · python/cpython

This can be simplified down to only define MS_WIN64, as the other variables are always defined unconditionally in this file.

Fixed.

(If Mingw isn't using the MSBuild files, then this change needs to go into the autoconf files for the generated pyconfig.h. This header file is only used by the PCbuild build files, not via make.)

If cpython is compiled by MSBuild and cython extension is compiled by mingw-w64 (which is the most common case, I think), it works. If someone (for example, msys2) wants to compile cpython itself by mingw-w64, many patches will be required anyway.