marshallers: ensure g_cclosure_marshal_VOID__VOIDv is used

If we set c_marshaller manually, then g_signal_newv() will not setup a
va_marshaller for us. However, if we provide c_marshaller as NULL, it will
setup both the c_marshaller (to g_cclosure_marshal_VOID__VOID) and
va_marshaller (to g_cclosure_marshal_VOID__VOIDv) for us.

gtk/gtktoggletoolbutton.c

@@ -144,7 +144,7 @@ gtk_toggle_tool_button_class_init (GtkToggleToolButtonClass *klass)
 		  G_SIGNAL_RUN_FIRST,
 		  G_STRUCT_OFFSET (GtkToggleToolButtonClass, toggled),
 		  NULL, NULL,
-		  g_cclosure_marshal_VOID__VOID,
+		  NULL,
 		  G_TYPE_NONE, 0);
 }