Avoid warnings from the job server

[Ewan Delanoy]

   My question is about a comment in GCC 5.2.0's Makefile (reproduced
   below).
   I don't understand how adding ": $(MAKE) ;" before the "$(unstage)"
   avoids warnings  from the GNU Make job server.
   AFAIK, the :$(MAKE) ; basically behaves like a comment. What difference
   will
   it make to the job server ? What kind of warning does it avoid ?

   # While making host and target tools, symlinks to the final stage must
   be
   # there, so $(unstage) should be run at various points.  To avoid
   excessive
   # recursive invocations of make, we "inline" them using a variable.
   These
   # must be referenced as ": $(MAKE) ; $(unstage)" rather than
   "$(unstage)"
   # to avoid warnings from the GNU Make job server.