- Sort the includes of pack.c, moving sys/*.h files near the top.
- Add a couple of missing #include lines, and remove the need for
custom -include options in the CFLAGS of the test Makefile.
- Remove the ad-hoc 'all' target, but keep its 'regress' bits for
testing.
- Convert the ad-hoc 'clean' target to proper CLEANFILES stuff,
so that the normal bsd.prog.mk machinery can clean up.
- Use `make -V .OBJDIR' to detect the place where 'pack' lives,
so that regress.t works both with and without 'make obj'.
Reviewed by: uqs
MFC after: 1 week
574fe75809