build on mingw - part 1

[totaam]

This part should be uncontroversial and does nothing unless:

• the preprocessor MINGW32 definition is present (header files)
• detects mingw uisng MINGW_PREFIX the environment variable in setup.py

[DirectXMan12]

looks good to me! Can you squash the 3 use gss.h on mingw commits into one use gss.h on mingw commit, and squash the pedantic checkers don't like bare except back into don't error out? After that, I'll merge. Thanks!

[totaam]

Can you squash the 3 use gss.h on mingw commits

Sorry but I have no idea how to squash commits using the github webui, otherwise I would have squashed them already..

[frozencemetery]

Pushed to master as 2a2b47b.

[DirectXMan12]

For future reference, just do it via the git CLI (git rebase -i) and then git push --force-with-lease