Windows: multithreaded runtime linking error

[MartinPdeS]

There appears to be a runtime linking error with the windows wheel build on GH-actions: windows-latest.
This is closely related to MinGW not being in the path.
What I already tried:
- statically link winpthread (unsuccessfull)
- adding Mingw library directory to path (unsuccessfull)
- removing OpenMP::OpenMP_CXX target link from CmakeList for windows build only (successfull)

I am leaving it this way for the moment, but it is on the to-do list!

[MartinPdeS]

Some interesting link for this specific issue:

• https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#adding-a-system-path

[MartinPdeS]

The issue was resolved in a previous commit that integrated the new python build system