Repalce rand_r() to fix MSVC compiling
Repalce rand_r() to fix MSVC compiling

BUG=aomedia:500

Change-Id: I8fc3b76925543da6928bf9c20c314dfe5f349317

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom