Fix panic message in SingletonContext.VisitAllModules

The panic should be printing the module info string from the
moduleInfo, not trying to Stringify the Module interface.

Test: manual
Change-Id: I1a2b7c15c4216518c76b909b25d50ac2eb7d1baa

singleton_ctx.go

@@ -223,7 +223,7 @@ func (s *singletonContext) VisitAllModules(visit func(Module)) {
 	defer func() {
 		if r := recover(); r != nil {
 			panic(newPanicErrorf(r, "VisitAllModules(%s) for module %s",
-				funcName(visit), visitingModule))
+				funcName(visit), s.context.moduleInfo[visitingModule]))
 		}
 	}()