gmp: add windows support

[star-hengxing]

Support msvc/clang toolchain build on msys2 or linux + msvc-wine.

Thanks by gpt-5.

[star-hengxing]

TODO

• Improve c23 patch
• windows arm64 support
• Some xmake internal error

[star-hengxing]

😒

test -n "$DJDIR" || exec 7<&0 </dev/null
exec 6>&1

error: @programdir\core\sandbox\modules\os.lua:273: ./configure: line 603: 0: Bad file descriptor

[star-hengxing]

/gemini summary
/gemini review

[gemini-code-assist]

It looks like you're trying to invoke the /gemini summary and /gemini review commands. Please note that these should be entered as separate commands in new comments. I am not able to execute commands directly from a comment like this. I can, however, respond to your comments and provide feedback on the pull request.

[star-hengxing]

/gemini review

[gemini-code-assist]

Code Review

This pull request adds support for building the gmp library on Windows using MSVC and Clang toolchains. The changes are extensive, involving modifications to the build process, new configurations, and platform-specific workarounds. While the overall approach is sound, I've found several issues, including a critical regression for macOS cross-compilation, some risky flag manipulations that could lead to build failures, and other areas for improvement in terms of robustness and clarity. Please see my detailed comments for suggestions on how to address these points.