compiler/glsl: Return progress from propagate_invariance()

Doing so allow you to easily tell what the pass did using the existing
infrastructure in the OPT macro.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10292>

src/compiler/glsl/propagate_invariance.cpp

@@ -113,13 +113,17 @@ ir_invariance_propagation_visitor::visit(ir_dereference_variable *ir)
    return visit_continue;
 }
 
-void
+bool
 propagate_invariance(exec_list *instructions)
 {
    ir_invariance_propagation_visitor visitor;
+   bool progress = false;
 
    do {
       visitor.progress = false;
       visit_list_elements(&visitor, instructions);
+      progress = progress || visitor.progress;
    } while (visitor.progress);
+
+   return progress;
 }