make windows code built with clangcl include the _posix source code. depot_tools excludes these source files now, so they need to be manually included. BUG=435 TESTED=clangcl local build on windows R=tpsiaki@google.com
make windows code built with clangcl include the _posix source code.
depot_tools excludes these source files now, so they need to be manually
included.
BUG=435
TESTED=clangcl local build on windows
R=tpsiaki@google.com

Review URL: https://webrtc-codereview.appspot.com/52419004

git-svn-id: a51711482b6ba0e1d1ab095578a045eeae45ac9a@1396 16f28f9a-4ce2-e073-06de-1de4eb20be90

labdong801/libyuv,godghdai/libyuv,labdong801/libyuv,lyx2014/libyuv_free,okumura/libyuv,lemenkov/libyuv,Bilibili/libyuv,xlncz/libyuv,okumura/libyuv,jpxiong/libyuv,yarrcc/libyuv-ios,lyx2014/yuv,okumura/libyuv,lyx2014/libyuv_free,PeterXu/libyuv,disigma/yuv,lemenkov/libyuv,lyx2014/libyuv_free,lyx2014/yuv,PeterXu/libyuv,lemenkov/libyuv,yarrcc/libyuv-ios,jpxiong/libyuv,godghdai/libyuv,lyx2014/yuv,yarrcc/libyuv-ios,jpxiong/libyuv,lyx2014/yuv,labdong801/libyuv,lemenkov/libyuv,xlncz/libyuv,yarrcc/libyuv-ios,xlncz/libyuv,Bilibili/libyuv,xlncz/libyuv,lyx2014/libyuv_free,disigma/yuv,Bilibili/libyuv,disigma/yuv,godghdai/libyuv,PeterXu/libyuv