directories to SUBDIR.${MK_TESTS} idiom
This is being done to pave the way for future work (and homogenity) in
^/projects/make-check-sandbox .
No functional change intended.
MFC after: 1 weeks
of the recent WARNS commits. The idea is:
1) FreeBSD id tags should follow vendor tags.
2) Vendor tags should not be compiled (though copyrights probably should).
3) There should be no blank line between including cdefs and __FBSDIF.
