Remove all the mingw specific code. We no longer used cygwin scons for building mingw packages, so just remove it. Also remove the explicit msys support and just patch the cygwin platform code instead, to simplify things.
Remove all the mingw specific code. We no longer used cygwin scons for building mingw packages, so just remove it. Also remove the explicit msys support and just patch the cygwin platform code instead, to simplify things.