ENH: Developing a dedicated compiler toolchain for windows scipy-meson builds

[carlkl]

Is your feature request related to a problem? Please describe.

rtools (chocolatey) is currently being used for CI windows scipy-meson builds. However, rtools is behind the msys2 ucrt64 gcc toolchain in terms of features and patches. The recent ucrt64 msys2 gcc toolchain contains more complete setting of patches targeting all kind of different issues. On the other hand all msys2/mingw-w64 packages are know as 'rolling release' packages. Reproducible builds are therefore difficult to achieve.

Describe the solution you'd like.

Developing and maintaining a win64 toolchain based on patches and build scripts of the https://github.com/msys2/MINGW-packages/ repository targeting the needs of a GCC based windows compiler toolchain with the greatest possible compatibility to MSVC. A fork of the UCRT64 compiler toolchain enables further changes/patches that appear necessary to be applied directly without waiting to be accepted upstream.

Another aspect is 32-bit support: it is possibility to develop a win32 (32-bit) toolchain with UCRT runtime support. A toolchain of this kind with Fortran support is not available yet: https://www.msys2.org/docs/environments/ from Msys2. See also this poll: scipy#16286

Describe alternatives you've considered.

leave the things as they are.

Additional context (e.g. screenshots, GIFs)

No response

[rgommers]

@carlkl thanks for the suggestion! I think it makes sense to do this in principle. Shall we move this issue to the main SciPy repo for more visibility? Now that we've merged Meson support into SciPy main after a year's worth of work on this repo, I think it's better to get more eyes on the next steps.