SSE2: slightly faster FTransformWHT
SSE2: slightly faster FTransformWHT

goes from 0.3% to 0.1% overall CPU time, but...

Change-Id: I4c9a92b1e1d6b58ed57c6b890366f1dbeaf84f84

ya7lelkom/libwebp,Aexyn/libwebp,PKRoma/libwebp,ya7lelkom/libwebp,ya7lelkom/libwebp,rxl194/libwebp,zofuthan/libwebp,imazen/libwebp,imazen/libwebp,imazen/libwebp,PKRoma/libwebp,PKRoma/libwebp,rxl194/libwebp,ttyangf/libwebp,Aexyn/libwebp,imazen/libwebp,zofuthan/libwebp,zofuthan/libwebp,yohunl/libwebp,yohunl/libwebp,PKRoma/libwebp,webmproject/libwebp,ttyangf/libwebp,ttyangf/libwebp,yohunl/libwebp,redengineer/libwebp,Aexyn/libwebp,zofuthan/libwebp,yohunl/libwebp,webmproject/libwebp,rxl194/libwebp,webmproject/libwebp,PKRoma/libwebp,redengineer/libwebp,ya7lelkom/libwebp,redengineer/libwebp,Aexyn/libwebp,Aexyn/libwebp,zofuthan/libwebp,redengineer/libwebp,ya7lelkom/libwebp,ttyangf/libwebp,yohunl/libwebp,ttyangf/libwebp,redengineer/libwebp,imazen/libwebp,PKRoma/libwebp,webmproject/libwebp,rxl194/libwebp,webmproject/libwebp,rxl194/libwebp