USE_GMAKE as a temporary band-aid for make(1) in FreeBSD 7 that now
remakes makefiles but cycles on lib/Makefile from tvision sources.
GNU make does not consider a target that exists, has no commands, is
older than its sources as out-of-date if no sources were actually remade and
thus does not cycle on such Makefiles. The fix for make(1) is coming soon.