DEP: remove code for supporting GCC <4 in Mingw32CCompiler

[lazka]

The last GCC 3.x release before 4.0 was 3.4 which was released 2004,
so 17 years ago.

Removes all code only used with those old toolchains.

This is an alternative to #20330

[mattip]

LGTM, assuming CI passes

[FFY00]

If this gets merged, we can go ahead and merge pypa/distutils#62.

[mattip]

What kind of backward compatibility promise does pypa/distutils (which I assume is merged frequently into pypa/setuptools)? Won't pypa/distutils#62 break every user of a NumPy older than this PR?

[FFY00]

I am not entirely sure about the backwards compatibility promises, but it shouldn't break unless you are using an old GCC version. I think that's reasonable. We can defer the decision to @jaraco, who should have a better handle on this.

[lazka]

What kind of backward compatibility promise does pypa/distutils (which I assume is merged frequently into pypa/setuptools)? Won't pypa/distutils#62 break every user of a NumPy older than this PR?

Are you talking about my proposal in pypa/distutils#62 (comment) ? The linked PR shouldn't change anything (and not sure if it is correct tbh...).

As for pypa/distutils, it's synced into setuptools, but not used unless SETUPTOOLS_USE_DISTUTILS is set, so its scope is very limited at this point. The MSYS2 project maintains a mingw-w64 fork of CPython and we have started to sync in pypa/distutils since CPython closed all distutils bug reports and is no longer accepting changes in that area, so it has some usage in MSYS2.

(I'm not aware of any other project besides MSYS2 building numpy with mingw-w64 though and we require quite a few patches to make it work, some are clang related though. )

[mattip]

Thanks for the cleanup @lazka

[lazka]

Thanks!