GList's used in legacy code were free'd using a g_list_foreach + g_list_free,
while we can just use g_list_free_full as per GLib 2.28.
So replace code where we were using this legacy codepath.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/576
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
Due to an accidental swap of an else statement and a preprocessor #else,
the output x coordinate is currently only set when not using the X11
windowing system, whoops.
https://bugzilla.gnome.org/show_bug.cgi?id=781902
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
