buildsystem: add -uninstalled.pc pkg-config file

For building against an uninstalled wayland-protocols tree

Signed-off-by: Reynaldo H. Verdejo Pinochet <reynaldo@osg.samsung.com>
Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
Signed-off-by: Derek Foreman <derekf@osg.samsung.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>
Reviewed-by: Jonas Ådahl <jadahl@gmail.com>