mesa: rewrite glPushAttrib/glPopAttrib to get rid of malloc
This was inevitable. This gets rid of the malloc/free calls and chaining each push group in a linked list. Now the whole attribute stack is declared statically in gl_context. Yes, this improves performance a lot. Acked-by:Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com> Part-of: <mesa/mesa!6946>