glsl: build stageref mask using IR, not symbol table
Instead of using symbol table, build mask by inspecting IR. This change is required by further patches to move resource list creation to happen later when symbol table does not exist anymore. Signed-off-by:Tapani Pälli <tapani.palli@intel.com> Reviewed-by:
Martin Peres <martin.peres@linux.intel.com> (cherry picked from commit ccaf37f4)