9cf8aa4584
Commit 0fd9e38175 fixed setting the out parameter for the x coordinate when using the X11 backend, but broke compilation when the backend is not available ... Really fix the issue by running the X11-specific code when the X11 backend is available and in use, and display the one-time warning otherwise. https://bugzilla.gnome.org/show_bug.cgi?id=781902