add support for Clang and GCC on Windows

[oltolm]

This adds support for Clang and GCC on Windows and fixes most of the warnings. I have also made audio and video work with Qt6 and plan to submit the changes in the next PR.

[oltolm]

BTW I do use MSYS2 to compile. I use the clang64 and mingw64 subsystems.

[oltolm]

ping