Add modified MPlayer Portfile to fix build errors

This PR includes a fixed Portfile for the MPlayer package to allow for a correct build on PowerPC. A fix allowing the port to build on macOS Sequoia (https://trac.macports.org/ticket/70804) breaks builds on at least Leopard if not also Snow Leopard, so it has been commented out. The patch for i386 builds has also been removed as it's out of scope.