folly: get building with gcc-4.7.1
folly: get building with gcc-4.7.1

Summary:
A lot of libstdc++-4.7 headers dropped includes of unistdc.h, so
we'll probably see more of these.

Test Plan: built folly

Reviewed By: simpkins@fb.com

FB internal diff: D508871

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