gbm: Add support for the new __driDriverGetExtensions interface.
gbm: Add support for the new __driDriverGetExtensions interface.

v2: Fix uninitialized variable use in the old-ABI case.

Reviewed-by: Chad Versace <a557f7f75bf28dc19ac99107f5cc7cd6b3fbdb1a@linux.intel.com> (v1)
Reviewed-by: Emil Velikov <4c996f2f093ddd0585a556460b4cc3ba555546ef@gmail.com>

zz85/glsl-optimizer,jbarczak/glsl-optimizer,tokyovigilante/glsl-optimizer,benaadams/glsl-optimizer,metora/MesaGLSLCompiler,jbarczak/glsl-optimizer,jbarczak/glsl-optimizer,mapbox/glsl-optimizer,metora/MesaGLSLCompiler,zeux/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,tokyovigilante/glsl-optimizer,metora/MesaGLSLCompiler,mapbox/glsl-optimizer,benaadams/glsl-optimizer,zz85/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,djreep81/glsl-optimizer,zz85/glsl-optimizer,mapbox/glsl-optimizer,zeux/glsl-optimizer,tokyovigilante/glsl-optimizer,tokyovigilante/glsl-optimizer,dellis1972/glsl-optimizer,bkaradzic/glsl-optimizer,djreep81/glsl-optimizer,mapbox/glsl-optimizer,jbarczak/glsl-optimizer,bkaradzic/glsl-optimizer,mcanthony/glsl-optimizer,djreep81/glsl-optimizer,bkaradzic/glsl-optimizer,bkaradzic/glsl-optimizer,mcanthony/glsl-optimizer,benaadams/glsl-optimizer,bkaradzic/glsl-optimizer,zeux/glsl-optimizer,zz85/glsl-optimizer,benaadams/glsl-optimizer,zeux/glsl-optimizer,wolf96/glsl-optimizer,zz85/glsl-optimizer,jbarczak/glsl-optimizer,zeux/glsl-optimizer,benaadams/glsl-optimizer,zz85/glsl-optimizer,djreep81/glsl-optimizer,benaadams/glsl-optimizer,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,wolf96/glsl-optimizer,djreep81/glsl-optimizer,dellis1972/glsl-optimizer,dellis1972/glsl-optimizer,mapbox/glsl-optimizer,dellis1972/glsl-optimizer,wolf96/glsl-optimizer