meson: don't build with USE_ELF_TLS on OpenBSD

OpenBSD does not have TLS

Fixes: a47c525f328 ("meson: build glx")
Signed-off-by: Jonathan Gray <jsg@jsg.id.au>
Reviewed-by: Eric Engestrom <eric@engestrom.ch>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5630>
1 file changed