gluTessCallback() expects an equivalent to a GFunc, but we pass
functions with arguments without casting. To get rid of warnings, cast
the callback function pointer to the expected type.
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