For a long time now MinGW has been unsupported and unmaintained and at this point, it looks like something that we should just leave behind and move on.
One of the big motivations for MinGW back in the day is that it was free compared to MSVC which was licensed based.
However, now that this is no longer true we have basically stopped updating the need CMake files.
Along with the CMake files, there are several patches to the extern libs needed to make this work. For example, see:
If we wanted to keep MinGW then we would need to make more custom patches to the external libs and this is not something our platform maintainers are willing to do.
So for the same reasons we removed Scons I think we should also remove MinGW.
Remove from git -- D2648
Remove from SVN
Rewrite Build docs for windows