MFC r273186,r273873:

r273186:

  Don't define rules based on PROGS if PROGS is empty.

  Reviewed by:	sjg, ngie
  Sponsored by:	EMC / Isilon Storage Division

r273873:

  Use the right depend file for each program.

  bsd.progs.mk generates a separate depend file for every program being
  built, but then it does not properly tell each submake to use those
  individual files.  Properly propagate the depend file to use.

  Discovered while preparing the update of atf to 0.21 and noticing that
  the test programs were not being relinked to the new library.

  This change is "make tinderbox" clean.