Include cpp only when needed
Include cpp only when needed

Summary:
D1008921 broke compilation for tao which uses folly/Portability.h
This diff guards the change for only c++ code. Not sure if this breaks the
definition of portability.

Test Plan: Compile tao, fbconfig -r folly and fbmake runtests

Reviewed By: simpkins@fb.com

FB internal diff: D1010967

@override-unit-failures

sonnyhu/folly,SammyK/folly,chjp2046/folly,nickhen/folly,rklabs/folly,stonegithubs/folly,mqeizi/folly,sakishum/folly,fw1121/folly,fw1121/folly,chjp2046/folly,bowlofstew/folly,kernelim/folly,colemancda/folly,romange/folly,guker/folly,reddit/folly,reddit/folly,constantine001/folly,leolujuyi/folly,clearlylin/folly,SammyK/folly,zhiweicai/folly,bikong2/folly,stonegithubs/folly,raphaelamorim/folly,reddit/folly,lifei/folly,Eagle-X/folly,Hincoin/folly,SeanRBurton/folly,wildinto/folly,ykarlsbrun/folly,charsyam/folly,bowlofstew/folly,mqeizi/folly,zhiweicai/folly,colemancda/folly,tempbottle/folly,sakishum/folly,sonnyhu/folly,wildinto/folly,loverszhaokai/folly,cppfool/folly,raphaelamorim/folly,doctaweeks/folly,arg0/folly,colemancda/folly,stonegithubs/folly,xzmagic/folly,bowlofstew/folly,SeanRBurton/folly,loversInJapan/folly,nickhen/folly,gaoyingie/folly,KSreeHarsha/folly,CJstar/folly,fw1121/folly,loverszhaokai/folly,gaoyingie/folly,clearlylin/folly,doctaweeks/folly,bowlofstew/folly,tomhughes/folly,clearlinux/folly,cole14/folly,rklabs/folly,charsyam/folly,raphaelamorim/folly,chjp2046/folly,unmeshvrije/C--,gaoyingie/folly,ykarlsbrun/folly,guker/folly,xzmagic/folly,hongliangzhao/folly,colemancda/folly,loversInJapan/folly,bsampath/folly,bowlofstew/folly,cppfool/folly,renyinew/folly,stonegithubs/folly,yangjin-unique/folly,constantine001/folly,gavioto/folly,gaoyingie/folly,loversInJapan/folly,mqeizi/folly,Orvid/folly,brunomorishita/folly,juniway/folly,KSreeHarsha/folly,juniway/folly,alexst07/folly,bsampath/folly,Eagle-X/folly,PPC64/folly,xzmagic/folly,Orvid/folly,Orvid/folly,wildinto/folly,juniway/folly,alexst07/folly,SeanRBurton/folly,CJstar/folly,loversInJapan/folly,project-zerus/folly,brunomorishita/folly,facebook/folly,Eagle-X/folly,mqeizi/folly,arg0/folly,Eagle-X/folly,hongliangzhao/folly,project-zerus/folly,mqeizi/folly,Hincoin/folly,tomhughes/folly,bobegir/folly,shaobz/folly,romange/folly,bobegir/folly,PPC64/folly,bsampath/folly,zhiweicai/folly,SammyK/folly,bikong2/folly,clearlinux/folly,romange/folly,theiver9827/folly,floxard/folly,tomhughes/folly,arg0/folly,floxard/folly,brunomorishita/folly,tempbottle/folly,gavioto/folly,floxard/folly,CJstar/folly,reddit/folly,yangjin-unique/folly,PoisonBOx/folly,Orvid/folly,clearlylin/folly,kernelim/folly,tempbottle/folly,lifei/folly,renyinew/folly,clearlinux/folly,gavioto/folly,clearlylin/folly,CJstar/folly,theiver9827/folly,SammyK/folly,gavioto/folly,doctaweeks/folly,Hincoin/folly,xzmagic/folly,clearlinux/folly,upsoft/folly,lifei/folly,renyinew/folly,sonnyhu/folly,rklabs/folly,guker/folly,bikong2/folly,bsampath/folly,brunomorishita/folly,zhiweicai/folly,nickhen/folly,arg0/folly,cole14/folly,colemancda/folly,hongliangzhao/folly,shaobz/folly,gaoyingie/folly,zhiweicai/folly,fw1121/folly,kernelim/folly,PPC64/folly,yangjin-unique/folly,floxard/folly,facebook/folly,tomhughes/folly,project-zerus/folly,Orvid/folly,doctaweeks/folly,raphaelamorim/folly,juniway/folly,renyinew/folly,unmeshvrije/C--,bikong2/folly,lifei/folly,sakishum/folly,SeanRBurton/folly,PoisonBOx/folly,tempbottle/folly,rklabs/folly,facebook/folly,upsoft/folly,Hincoin/folly,bobegir/folly,raphaelamorim/folly,yangjin-unique/folly,kernelim/folly,unmeshvrije/C--,cole14/folly,facebook/folly,loversInJapan/folly,constantine001/folly,loverszhaokai/folly,rklabs/folly,nickhen/folly,leolujuyi/folly,romange/folly,charsyam/folly,renyinew/folly,bikong2/folly,xzmagic/folly,sakishum/folly,sonnyhu/folly,SammyK/folly,brunomorishita/folly,floxard/folly,cppfool/folly,loverszhaokai/folly,PoisonBOx/folly,leolujuyi/folly,upsoft/folly,guker/folly,juniway/folly,sakishum/folly,fw1121/folly,reddit/folly,project-zerus/folly,sonnyhu/folly,PPC64/folly,Hincoin/folly,kernelim/folly,nickhen/folly,cppfool/folly,theiver9827/folly,upsoft/folly,theiver9827/folly,bsampath/folly,hongliangzhao/folly,ykarlsbrun/folly,shaobz/folly,wildinto/folly,PPC64/folly,shaobz/folly,ykarlsbrun/folly,alexst07/folly,SeanRBurton/folly,upsoft/folly,clearlylin/folly,charsyam/folly,cole14/folly,chjp2046/folly,clearlinux/folly,alexst07/folly,PoisonBOx/folly,lifei/folly,loverszhaokai/folly,unmeshvrije/C--,bobegir/folly,alexst07/folly,facebook/folly,CJstar/folly,leolujuyi/folly,tomhughes/folly,theiver9827/folly,unmeshvrije/C--,Eagle-X/folly,guker/folly,KSreeHarsha/folly,unmeshvrije/C--,arg0/folly,romange/folly,hongliangzhao/folly,stonegithubs/folly,cppfool/folly,project-zerus/folly,ykarlsbrun/folly,PoisonBOx/folly,shaobz/folly,KSreeHarsha/folly,chjp2046/folly,wildinto/folly,constantine001/folly,doctaweeks/folly,yangjin-unique/folly,cole14/folly,leolujuyi/folly,gavioto/folly,bobegir/folly,KSreeHarsha/folly,constantine001/folly,tempbottle/folly