We set this in deqp-runner runs to disable Mesa debug/debugoptimized builds printing to stderr for expected GL test behavior, and with the addition of dEQP-EGL mapi got very verbose. Move it to a call_once() too to avoid data races. Acked-by: Eric Engestrom <eric@engestrom.ch> Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10240>