I\'m trying to apply this patch to GCC on MinGW to get it to compile GDC 2, but I don\'t know how. (I\'m still new to the internals of GCC, and even to *nix tools in general
Take a look at the patch manual pages. Just type man patch in a terminal window... typically i think you want to do a patch -p0 -i your_file.diff.
man patch
patch -p0 -i your_file.diff