clutter: Prefer the X11 backend to the Wayland one
clutter: Prefer the X11 backend to the Wayland one

If clutter is built with both X11 and Wayland support, prefer the
(more complete for now) X11 backend. This matches GTK+'s current
ordering.

This allows distributions to ship a clutter version with both backends
built, and using an envvar to switch to the wayland backend and test
applications.

In the future, applications would be able to choose which backend
they prefer and in which order.

https://bugzilla.gnome.org/show_bug.cgi?id=695838

djdeath/clutter,jigpu/clutter,Distrotech/clutter,collects/clutter,ebassi/clutter,djdeath/clutter-android,jigpu/clutter,GNOME/clutter,heysion/clutter-clone,Distrotech/clutter,GNOME/clutter,djdeath/clutter-android,djdeath/clutter-android,heysion/clutter-clone,Distrotech/clutter,GNOME/clutter,djdeath/clutter,collects/clutter,djdeath/clutter,collects/clutter,collects/clutter,djdeath/clutter-android,ebassi/clutter,heysion/clutter-clone,ebassi/clutter,djdeath/clutter-android,ebassi/clutter,jigpu/clutter,jigpu/clutter,Distrotech/clutter,djdeath/clutter,GNOME/clutter,djdeath/clutter,collects/clutter,Distrotech/clutter,GNOME/clutter,heysion/clutter-clone,jigpu/clutter,Distrotech/clutter,ebassi/clutter,djdeath/clutter,heysion/clutter-clone,jigpu/clutter