The exact command used to migrate source files was:
git ls-files | grep 'src/.*\.[ch]$' | xargs grep -l INCBIN | xargs python3 migrate_incgfx.py
The Makefile rules were cleaned up manually by looking for graphics
rules and keeping only those ending with '\' (what the migration script
calls a "Multi-line rule"). You may think some of wallpaper rules could
be removed, but they're inputs for the '@cat $^ >$@' rules which are
currently unable to be migrated to 'INCGFX'.
