Of note, 'devel' on FreeBSD usually means 'bleeding edge', not 'development libraries and headers'
Update: I added `-I/path/to/allegro/include` to every compilation line in the Makefile since that's why allegro5/allegro.h wasn't being found and get errors. I'm not on that laptop at the moment so I can't yet add the actual error message here, but I'll edit it in when I turn it on.