port aom_thread.h change from libvpx/nextgenv2
port aom_thread.h change from libvpx/nextgenv2

Change-Id: Ib81aa1f1eb7a41116a9a94696925c7d5038e21bd

GrokImageCompression/aom,mbebenita/aom,mbebenita/aom,mbebenita/aom,luctrudeau/aom,luctrudeau/aom,luctrudeau/aom,GrokImageCompression/aom,mbebenita/aom,mbebenita/aom,smarter/aom,luctrudeau/aom,mbebenita/aom,smarter/aom,smarter/aom,luctrudeau/aom,mbebenita/aom,smarter/aom,GrokImageCompression/aom,smarter/aom,luctrudeau/aom,GrokImageCompression/aom,smarter/aom,mbebenita/aom,GrokImageCompression/aom,GrokImageCompression/aom,mbebenita/aom