Do not force use of "gmake" -- but propagate whichever command was used to start the top-level make.  This way users on e.g.
Mac OS X won't have to create a special symlink to build, but can instead just use the command "gnumake" (as opposed to "make" og "gmake")

Merged from tholo's branch http://svn.freeswitch.org/svn/freeswitch/branches/tholo rev 2796, thanks tholo.

git-svn-id: http://svn.freeswitch.org/svn/freeswitch/trunk@2815 d0543943-73ff-0310-b7d9-9358b9ac24b2