Restore argument usage line.

diff -r 715cb1bf8619 modules/graphics/src/main/native-glass/gtk/glass_gtkcompat.cpp
--- a/modules/graphics/src/main/native-glass/gtk/glass_gtkcompat.cpp Fri Dec 18 21:32:44 2015 -0500
+++ b/modules/graphics/src/main/native-glass/gtk/glass_gtkcompat.cpp Sat Dec 19 11:12:22 2015 -0500
@@ -355,6 +355,7 @@
 
 static void
 configure_opaque_window(GtkWidget *window) {
+ (void) window;
 
     gtk_widget_set_visual(window,
                           gdk_screen_get_system_visual(