gh-141671: PyMODINIT_FUNC: apply __declspec(dllexport) on Windows

[encukou]

• Issue: PyMODINIT_FUNC does not apply __declspec(dllexport) on Windows #141671

[encukou]

cc @jaraco / @pfmoore: what are your thoughts on removing /EXPORT from setuptools/distutils on Python 3.15+?

[zooba]

I'm not 100% sure about this... don't we need it for our own exports?

[encukou]

Only for Py_ENABLE_SHARED -- see #99888 that added the #else.

[zooba]

Ah, I see we do these checks again everywhere else we use the macros. No problem them.

[pfmoore]

TBH, I have no view. My knowledge of C is very out of date, so I wouldn't trust anything I might say anyway...

[da-woods]

The /EXPORT from setuptools has definitely caused Cython an amount of pain before (although some of that was self-inflicted....). It'd be nice not to have to define PyInit_ just to to make the name exist. Although I suspect we can't really avoid it in a realistic timeline.

(Edit: admittedly we also aren't the people that it's designed to help either)