Add GC_FLAGS in Makefile, don't build GC if already built.
Add GC_FLAGS in Makefile, don't build GC if already built.

marcusnaslund/rock,thomasfanell/rock,ooc-lang/rock,cogneco/rock,jonathanudd/rock,fredrikbryntesson/rock,magic-lang/rock,fasterthanlime/rock,zhaihj/rock,ds84182/rock,ds84182/rock,shamanas/rock,davidhesselbom/rock,cogneco/rock,thomasfanell/rock,marcusnaslund/rock,davidhesselbom/rock,shamanas/rock,jonathanudd/rock,zhaihj/rock,fredrikbryntesson/rock,ooc-lang/rock,magic-lang/rock,fasterthanlime/rock