Detect clang in folly/Portability.h
Detect clang in folly/Portability.h

Summary: The fix in D2283221 was specific to a bug in gcc 4.8 but the macro was failing
to filter out clang compilers.

Reviewed By: @yfeldblum

Differential Revision: D2340160

Eagle-X/folly,facebook/folly,bowlofstew/folly,sonnyhu/folly,loversInJapan/folly,loversInJapan/folly,Orvid/folly,gavioto/folly,KSreeHarsha/folly,PoisonBOx/folly,arg0/folly,floxard/folly,Hincoin/folly,tomhughes/folly,rklabs/folly,yangjin-unique/folly,loversInJapan/folly,upsoft/folly,juniway/folly,bobegir/folly,tomhughes/folly,CJstar/folly,arg0/folly,mqeizi/folly,zhiweicai/folly,gaoyingie/folly,clearlylin/folly,juniway/folly,stonegithubs/folly,rklabs/folly,alexst07/folly,raphaelamorim/folly,SammyK/folly,fw1121/folly,brunomorishita/folly,PoisonBOx/folly,juniway/folly,CJstar/folly,SeanRBurton/folly,Hincoin/folly,upsoft/folly,tempbottle/folly,upsoft/folly,constantine001/folly,yangjin-unique/folly,yangjin-unique/folly,constantine001/folly,rklabs/folly,constantine001/folly,SeanRBurton/folly,gavioto/folly,stonegithubs/folly,gaoyingie/folly,bikong2/folly,zhiweicai/folly,gaoyingie/folly,CJstar/folly,SeanRBurton/folly,bobegir/folly,raphaelamorim/folly,bowlofstew/folly,floxard/folly,rklabs/folly,raphaelamorim/folly,sakishum/folly,arg0/folly,theiver9827/folly,mqeizi/folly,tempbottle/folly,leolujuyi/folly,tomhughes/folly,alexst07/folly,SeanRBurton/folly,renyinew/folly,Eagle-X/folly,sakishum/folly,sonnyhu/folly,guker/folly,brunomorishita/folly,loversInJapan/folly,Eagle-X/folly,Orvid/folly,PoisonBOx/folly,lifei/folly,charsyam/folly,CJstar/folly,tempbottle/folly,KSreeHarsha/folly,charsyam/folly,SeanRBurton/folly,tomhughes/folly,SammyK/folly,Orvid/folly,Hincoin/folly,theiver9827/folly,renyinew/folly,lifei/folly,renyinew/folly,bobegir/folly,brunomorishita/folly,leolujuyi/folly,fw1121/folly,Orvid/folly,reddit/folly,SammyK/folly,constantine001/folly,fw1121/folly,bikong2/folly,loversInJapan/folly,gavioto/folly,alexst07/folly,alexst07/folly,yangjin-unique/folly,mqeizi/folly,reddit/folly,arg0/folly,guker/folly,leolujuyi/folly,zhiweicai/folly,constantine001/folly,stonegithubs/folly,juniway/folly,facebook/folly,guker/folly,sakishum/folly,floxard/folly,facebook/folly,fw1121/folly,sakishum/folly,reddit/folly,PoisonBOx/folly,stonegithubs/folly,upsoft/folly,zhiweicai/folly,lifei/folly,PPC64/folly,tempbottle/folly,stonegithubs/folly,facebook/folly,floxard/folly,sonnyhu/folly,guker/folly,PPC64/folly,KSreeHarsha/folly,gaoyingie/folly,theiver9827/folly,Hincoin/folly,Hincoin/folly,floxard/folly,PoisonBOx/folly,tomhughes/folly,KSreeHarsha/folly,reddit/folly,Eagle-X/folly,mqeizi/folly,hongliangzhao/folly,theiver9827/folly,raphaelamorim/folly,rklabs/folly,bikong2/folly,gaoyingie/folly,lifei/folly,bowlofstew/folly,sonnyhu/folly,charsyam/folly,upsoft/folly,hongliangzhao/folly,reddit/folly,sakishum/folly,juniway/folly,bowlofstew/folly,yangjin-unique/folly,tempbottle/folly,clearlylin/folly,bobegir/folly,Orvid/folly,PPC64/folly,renyinew/folly,leolujuyi/folly,clearlylin/folly,Eagle-X/folly,bikong2/folly,gavioto/folly,facebook/folly,brunomorishita/folly,brunomorishita/folly,guker/folly,SammyK/folly,arg0/folly,alexst07/folly,charsyam/folly,theiver9827/folly,bowlofstew/folly,raphaelamorim/folly,CJstar/folly,gavioto/folly,zhiweicai/folly,bobegir/folly,fw1121/folly,mqeizi/folly,leolujuyi/folly,hongliangzhao/folly,bikong2/folly,KSreeHarsha/folly,lifei/folly,hongliangzhao/folly,clearlylin/folly,renyinew/folly,PPC64/folly,sonnyhu/folly,hongliangzhao/folly,SammyK/folly,clearlylin/folly,PPC64/folly