branches: 1.2.2;
remove the recently added files or added entries for what is
./usr/include/$MACHINE and automatically add it.

add sun68k for sun2/sun3. tested on about 12 platforms.

there may be more failures to figure out but this should make
them all special cases rather than always expected cases.

fortunately, most builds don't see to hit these issues for
reasons i haven't determined yet.

ensure that all include dirs are created before make includes runs.

separate the compat vs per-arch -ness of the mtree lists. merge the
mips64 mtree files into a single file.