Some of the marshallers we generate in `clutter-marshal.list` are also
available in GLib, so we don't need to generate them ourselves. Even
more, by passing NULL to `g_signal_new` in these cases will actually
internally optimize this even more by also setting the valist
marshaller, which is a little bit faster than the regular marshalling
using `GValue` and libffi.
https://gitlab.gnome.org/GNOME/mutter/merge_requests/700
Commit 25f416c13db added additional compilation warnings, including
-Werror=return-type. There are several places where this results
in build failures if `g_assert_not_reached()` is disabled at compile
time and the compiler misses a return value.
https://gitlab.gnome.org/GNOME/mutter/issues/447
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
