Rygel should not have a dependency on X11 when no GUI (ie GTK+) is used
in src/rygel/meson.build, there is an unconditional dependency on X11 library. This is only required because of the X.init_threads call in src/rygel/application.vala which is not required when building without GTK+. Here is a quite simple patch proposal to make this dependency optional, conditioned by use of GTK+ GUI which can be useful on headless servers.
Please review and apply if correct.