gtk: Ignore gtk_show_uri() deprecation warnings

https://bugzilla.gnome.org/show_bug.cgi?id=778726

gtk/gtkprintoperation-unix.c

@@ -200,6 +200,7 @@ shell_command_substitute_file (const gchar *cmd,
   return g_string_free (final, FALSE);
 }
 
+G_GNUC_BEGIN_IGNORE_DEPRECATIONS
 static void
 gtk_print_operation_unix_launch_preview (GtkPrintOperation *op,
                                          cairo_surface_t   *surface,
@@ -341,6 +342,7 @@ gtk_print_operation_unix_launch_preview (GtkPrintOperation *op,
   g_free (data);
   g_free (settings_filename);
 }
+G_GNUC_END_IGNORE_DEPRECATIONS
 
 static void
 unix_finish_send  (GtkPrintJob  *job,