[Suggestion] Add support for building skylark with the MinGW-w64 compiler

[ghost]

If you can, please add GNU Makefiles for building skylark with the MinGW-w64 compiler. I'm running on a less powerful machine and can't install MSVC, but I have no problems with compiling software using the MinGW-w64 compiler and mingw32-make so far. Skylark is a C program and the code base is not large too, so I think it will be OK on my machine.