This improves the general building experience by integrating with the
newly created `sourceball` for windows. Most fixes involves either
adding `#ifdef WIN32` or replacing GCC-specific extensions with more
portable solutions.
Has been tested with MSVC 15 and MinGW64.
I needed that for my new super user-friendly and cool loading super screen, I'll finish the softgm version tomorrow.
Also took care of some warning I had.