We recently upgraded wayland.xml to 1.10, although we're supposed to support libwayland as old as 1.6
This should have been fine, however having a newer version of wayland.xml than libwayland is only supported if only the core includes are used. I.e. wayland-client-core instead of wayland-client. Ditto for server.
Consequently, libwayland doesn't currently build with libwayland 1.9 or older.