libyuv: Include foo_posix.cc in the gn build, like it's done in the gyp build.
libyuv: Include foo_posix.cc in the gn build, like it's done in the gyp build.

This is required to get things linking in clang/win. Medium-term, we should
clean libyuv up to not require _posix files on non-posix.

Reviewed at https://webrtc-codereview.appspot.com/52069004/

BUG=496928

Review URL: https://webrtc-codereview.appspot.com/54689004
eterrao/libyuv,wmiller848/libyuv,zephyroal/libyuv,dong83615/libyuv,Evgeniy-Odesskiy/libyuv,ddpatel2606/libyuv,gengchenglin/libyuv,lyx2014/libyuv,muslim1977/libyuv,huangxueqin/libyuv,wmiller848/libyuv,ksophocleous/libyuv,patrickcusack/libyuv,weifud/libyuv,sitoumbaz/libyuv,gavinljj/libyuv,biotrump/libyuv,zothen/libyuv,alfatraining/libyuv,sigysmund/libyuv,binsys/libyuv,koxiong/libyuv,skyofdwarf/libyuv,xiongdaofu/libyuv,lyx2014/libyuv,kiwifig/libyuv,eterrao/libyuv,jeyluta/libyuv,virneo/libyuv,andriy-yermakov/libyuv,andriy-yermakov/libyuv,Evgeniy-Odesskiy/libyuv,ericma2014/libyuv,wanggenggz/libyuv,lemoon/libyuv,Locnath/libyuv,Ariesnix/libyuv,zijay0822/libyuv,lemoon/libyuv,jrdeng/libyuv,wanggenggz/libyuv,Shamim1977/libyuv,zhuolinho/libyuv,xuruhao/libyuv,buliaoyin/libyuv,hongqingquan/libyuv,ksophocleous/libyuv,tectronics/libyuv,AshwanthSelvam/libyuv,pecoco/libyuv,Miliox/libyuv,liuzhe02/libyuv,codyc/libyuv,jhanay/libyuv,changchang/libyuv,Malek44/libyuv,fjyihan/libyuv,FAHADSUST/libyuv,Evgeniy-Odesskiy/libyuv,zpc930/libyuv,Ariesnix/libyuv,KIHOSONG/libyuv,gavinljj/libyuv,sepcity/libyuv,zj2089/libyuv,biotrump/libyuv,jeyluta/libyuv,theunreplicated/libyuv,ericma2014/libyuv,bluceldg/libyuv,EdgarMora/libyuv,katepanping/libyuv,sepcity/libyuv,sateeshyegireddi/libyuv,todostreaming/libyuv,sigysmund/libyuv,envyen/libyuv,swak/libyuv,todostreaming/libyuv,jrdeng/libyuv,patrickcusack/libyuv,changchang/libyuv,zothen/libyuv,muslim1977/libyuv,happy-star/libyuv,elkpi/libyuv,zhuolinho/libyuv,Locnath/libyuv,Locnath/libyuv,jhanay/libyuv,se7en3rd/libyuv,biotrump/libyuv,alfatraining/libyuv,bluceldg/libyuv,KIHOSONG/libyuv,buliaoyin/libyuv,polyzz/libyuv,todostreaming/libyuv,drybeans/libyuv,danilogr/libyuv,changchang/libyuv,huangxueqin/libyuv,Eikan/libyuv,happy-star/libyuv,envyen/libyuv,jrdeng/libyuv,binsys/libyuv,sepcity/libyuv,envyen/libyuv,lyx2014/libyuv,xiongdaofu/libyuv,cjr1983/libyuv,Miliox/libyuv,torodavit/libyuv,AshwanthSelvam/libyuv,torodavit/libyuv,fjyihan/libyuv,Shamim1977/libyuv,patrickcusack/libyuv,sigysmund/libyuv,se7en3rd/libyuv,mannuray/libyuv,zj2089/libyuv,skyofdwarf/libyuv,katepanping/libyuv,virneo/libyuv,hushuitian/libyuv,polyzz/libyuv,hushuitian/libyuv,stephenyin/libyuv,ddpatel2606/libyuv,gavinljj/libyuv,jeyluta/libyuv,FAHADSUST/libyuv,cjr1983/libyuv,xuruhao/libyuv,sitoumbaz/libyuv,pecoco/libyuv,AshwanthSelvam/libyuv,oiramario/libyuv,sateeshyegireddi/libyuv,zpc930/libyuv,heyfluke/libyuv,lcwyylcwyy/libyuv,Malek44/libyuv,oiramario/libyuv,katepanping/libyuv,liuzhe02/libyuv,kpgalligan/libyuv,tectronics/libyuv,theunreplicated/libyuv,leeslove/libyuv,dong83615/libyuv,zephyroal/libyuv,zijay0822/libyuv,eterrao/libyuv,Ariesnix/libyuv,torodavit/libyuv,codyc/libyuv,JuannyWang/libyuv,kpgalligan/libyuv,cjr1983/libyuv,codyc/libyuv,koxiong/libyuv,foolab/libyuv,EdgarMora/libyuv,binsys/libyuv,heyfluke/libyuv,dreamcoder/libyuv,bluceldg/libyuv,se7en3rd/libyuv,nanguantong/libyuv,zhuolinho/libyuv,elkpi/libyuv,swak/libyuv,zj2089/libyuv,fjyihan/libyuv,weifud/libyuv,zothen/libyuv,sitoumbaz/libyuv,platoon-code/libyuv,happy-star/libyuv,zpc930/libyuv,platoon-code/libyuv,hongqingquan/libyuv,jhanay/libyuv,ericma2014/libyuv,buliaoyin/libyuv,gengchenglin/libyuv,virneo/libyuv,alfatraining/libyuv,swak/libyuv,mannuray/libyuv,oiramario/libyuv,KIHOSONG/libyuv,Eikan/libyuv,dreamcoder/libyuv,JuannyWang/libyuv,BigMing001/libyuv,muslim1977/libyuv,mayurAzoi/libyuv,wanggenggz/libyuv,hongqingquan/libyuv,nanguantong/libyuv,weifud/libyuv,gengchenglin/libyuv,yosoymin/libyuv,tectronics/libyuv,koxiong/libyuv,EdgarMora/libyuv,huangxueqin/libyuv,lcwyylcwyy/libyuv,dong83615/libyuv,FAHADSUST/libyuv,kiwifig/libyuv,zijay0822/libyuv,zephyroal/libyuv,heyfluke/libyuv,alfatraining/libyuv,lemoon/libyuv,drybeans/libyuv,yosoymin/libyuv,hushuitian/libyuv,nanguantong/libyuv,Shamim1977/libyuv,mannuray/libyuv,leeslove/libyuv,yosoymin/libyuv,theunreplicated/libyuv,xuruhao/libyuv,wmiller848/libyuv,elkpi/libyuv,stephenyin/libyuv,Miliox/libyuv,mayurAzoi/libyuv,Eikan/libyuv,polyzz/libyuv,JuannyWang/libyuv,xiongdaofu/libyuv,liuzhe02/libyuv,ksophocleous/libyuv,stephenyin/libyuv,platoon-code/libyuv,kpgalligan/libyuv,BigMing001/libyuv,danilogr/libyuv,mayurAzoi/libyuv,drybeans/libyuv,BigMing001/libyuv,lcwyylcwyy/libyuv,sateeshyegireddi/libyuv,danilogr/libyuv,foolab/libyuv,Malek44/libyuv,ddpatel2606/libyuv,leeslove/libyuv,pecoco/libyuv,foolab/libyuv,skyofdwarf/libyuv,andriy-yermakov/libyuv,kiwifig/libyuv,dreamcoder/libyuv