package/libglfw: bump to 3.3.6 and enable Wayland/libGLES support

Signed-off-by: Andre Renaud <andre@ignavus.net>
[Arnout: reorder .mk so conditional parts come after unconditional, and
use += within conditions]
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>