Makepatch is a patch manager for pacman packages.
Initialize working directory:
tar xf tarball.tar.gz
makepatch init extracted
Edit existing patches:
vim patches/001/some/source/file.c
makepatch diff 001
makepatch refresh
Create new patches:
cp -r patches/{001,002}
vim patches/002/edit/files.c
makepatch diff 002 > 002-name.patch