Import rintex.c from https://github.com/toddfries/OpenBSD-lib-patches/raw/master/libc/string/rindex.c
Expose rindex via string.h
Import https://github.com/toddfries/OpenBSD-lib-patches/raw/master/libc/string/swab.c
Fix up string.h so that rindex works
Fix up unistd.h with implied size_t to make swab build
stub math.h. Harvest the precious setjmp stuff that the KDB uses
Experiment with building Lua