OpenGL: Build with GCC for Adreno compatibility

Summary:
Clang treats const char type differently (view processed code to see).
For compatibility against Adreno prebuilts, we will build libopengl
and it's wrappers with gcc

Test Plan: verified

Reviewers: randall.rushing, synergy

Reviewed By: synergy

Differential Revision: http://review.codefirex.com/D86