Slackware64's pmake is broken: the includes /usr/share/mk/*.mk all say
things like 'LIBC=/usr/lib64/libc.a' (the lib should be lib64). These
files *have* to exist, whether they're actually needed or not (and they're
not, since they're static libs and we're building dynamic binaries).

This directory contains fixed versions of the mk includes, for pmake's -m
option to use.