fixes for the compilation warnings with Sun CC:

1. some fixes for "String literal to char * conversion" warnings (many
   more left in the *.xpm files)
2. fixes for "assignment of function to extern "C" function"
3. a few other miscellaneous ones


git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@13478 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/gtk1/win_gtk.c

@@ -852,7 +852,7 @@ gtk_pizza_forall (GtkContainer *container,
 
     g_return_if_fail (container != NULL);
     g_return_if_fail (GTK_IS_PIZZA (container));
-    g_return_if_fail (callback != NULL);
+    g_return_if_fail (callback != (GtkCallback)NULL);
 
     pizza = GTK_PIZZA (container);