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
it fully passes the GNU timeout regression tests, it is written in a mostly
portable way (only signal parsing is relying on non portable structures)
Phabric: D377