IsFifoBusy is obsolete in recent revisions, no way to apply this patch since the former code for IsFifoBusy no longer exists. With Marco's improvement to the fifo code (currently a wip) this will no longer be necessary and games should run at their proper speeds.
You will have to apply the patch on a revision prior to r6554 or wait until the new fifo code is complete. Patches are applied with Tortoise SVN, right click the directory with the local copy of the source, click "Tortoise SVN" and "Apply Patch". Then just select the patch file and patch all or selected files and compile the source code. You can also ask Lectrode or another member who is compiling builds, to compile and upload a specific build.
You will have to apply the patch on a revision prior to r6554 or wait until the new fifo code is complete. Patches are applied with Tortoise SVN, right click the directory with the local copy of the source, click "Tortoise SVN" and "Apply Patch". Then just select the patch file and patch all or selected files and compile the source code. You can also ask Lectrode or another member who is compiling builds, to compile and upload a specific build.