ir_structure_splitting: New pass to chop structures into their components.

This doesn't do anything if your structure goes through an uninlined
function call or if whole-structure assignment occurs.  As such, the
impact is limited, at least until we do some global copy propagation
to reduce whole-structure assignment.

src/glsl/linker.cpp

@@ -1287,6 +1287,7 @@ link_shaders(struct gl_shader_program *prog)
 
 	 progress = do_function_inlining(ir) || progress;
 	 progress = do_dead_functions(ir) || progress;
+	 progress = do_structure_splitting(ir) || progress;
 	 progress = do_if_simplification(ir) || progress;
 	 progress = do_copy_propagation(ir) || progress;
 	 progress = do_dead_code_local(ir) || progress;