Because this is just building, didn't not used by CTS runner,
So enable glx=xlib in this build variant
Signed-off-by: Yonggang Luo <luoyonggang@gmail.com> Reviewed-by: Eric Engestrom <eric@igalia.com> Reviewed-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19258>