Fix high bit depth test build on macosx.
Fix high bit depth test build on macosx.

Change-Id: I8a5288d82e9dda32bf5e47a17c0ee88e4da0b1c5

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