The presence of the .SECONDARY directive caused thing to not always
be correctly rebuilt.  Mentioning the object files explicitly as
targets gives the desired result of make not deleting them without
unpleasant side-effects.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@22422 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b