According to the bug report that patch is already applied in the fpc 2.3.1. So you can:
1) download fpc 2.3.1 and use it
2) install subversion, checkout paticular revision (which you have at moment), and apply patch using patch command: patch -p0 your_fpc_dir < you_patch.patch
Or if you are using windows you can install TortoiseSVN client and apply patch using it.