common.gypi: remove GCC_VERSION on OSX
common.gypi: remove GCC_VERSION on OSX

this isn't needed anymore, remove it.

bsn069/luvit,rjeli/luvit,sousoux/luvit,sousoux/luvit,connectFree/lev,zhaozg/luvit,AndrewTsao/luvit,kaustavha/luvit,kaustavha/luvit,DBarney/luvit,AndrewTsao/luvit,luvit/luvit,DBarney/luvit,DBarney/luvit,AndrewTsao/luvit,rjeli/luvit,GabrielNicolasAvellaneda/luvit-upstream,sousoux/luvit,sousoux/luvit,sousoux/luvit,boundary/luvit,luvit/luvit,boundary/luvit,connectFree/lev,rjeli/luvit,kaustavha/luvit,boundary/luvit,boundary/luvit,bsn069/luvit,bsn069/luvit,rjeli/luvit,GabrielNicolasAvellaneda/luvit-upstream,DBarney/luvit,zhaozg/luvit,GabrielNicolasAvellaneda/luvit-upstream,boundary/luvit,GabrielNicolasAvellaneda/luvit-upstream,boundary/luvit,sousoux/luvit