autotools: use correct gl.pc LIBS when using glvnd
This is more of a hack, since glvnd itself should be providing the file. Until that happens, ensure the libs is correctly set to -lGL CC: <mesa-stable@lists.freedesktop.org> Signed-off-by:Emil Velikov <emil.velikov@collabora.com> Reviewed-by:
Adam Jackson <ajax@redhat.com>