Since commit 0eab73dc, actors are only allocated when they are actually
visible. While this generally works well, it breaks - because of *course*
it does - ClutterClones when the clone source (or any of its ancestors)
is hidden.
Force an allocation in that case to allow the clone's paint to work as
intended.
https://gitlab.gnome.org/GNOME/mutter/issues/683
In cogl use cogl-config.h and in clutter use clutter-build-config.h. We
can't use clutter-config.h in clutter because its already used and
installed.
https://bugzilla.gnome.org/show_bug.cgi?id=768976