Does not compile with MinGW

[takase1121]

The makefile defaults to MSVC tools when Windows is detected, maybe there is a way to make it detect if its running in MSYS2 and switch to GCC automatically?

[lammertb]

MinGW is currently untested. The original MinGW has it last significant update in the SourceForge repository in 2013 and will not be supported.

The 64 bit fork mingw-64 will be supported in the near future, but I have to build a proper virtual machine environment for it first.

The Makefile structure needs to be changed for that, but I am planning that anyway to make cross-compilation for other environments than the build environment smoother than with the current setup.