Fix a build issue for a test
Fix a build issue for a test

This commit adds #ifdef __cpluscplus guard in odintrin.h to enable
the build of related test in C++.

Change-Id: I89ddbdd56b10657ac7e4c71e2f26ed791550b493

smarter/aom,shacklettbp/aom,mbebenita/aom,thdav/aom,luctrudeau/aom,mbebenita/aom,luctrudeau/aom,smarter/aom,shacklettbp/aom,GrokImageCompression/aom,mbebenita/aom,smarter/aom,mbebenita/aom,thdav/aom,GrokImageCompression/aom,smarter/aom,thdav/aom,smarter/aom,mbebenita/aom,thdav/aom,mbebenita/aom,mbebenita/aom,luctrudeau/aom,thdav/aom,luctrudeau/aom,luctrudeau/aom,thdav/aom,mbebenita/aom,GrokImageCompression/aom,shacklettbp/aom,shacklettbp/aom,shacklettbp/aom,shacklettbp/aom,luctrudeau/aom,mbebenita/aom,GrokImageCompression/aom,GrokImageCompression/aom,smarter/aom,GrokImageCompression/aom