ci: Improve MinGW/MSYS Makefiles mingw.osdn.io job environments
Set PATH, MSYSTEM, and MAKE_MODE environment variables the way the
MinGW/MSYS 1.0 distribution from mingw.osdn.io does in its bash prompt.
Set PATH, MSYSTEM, and MAKE_MODE environment variables the way the
MinGW/MSYS 1.0 distribution from mingw.osdn.io does in its bash prompt.