The render-nodes case is untested.

v2: Add a flag for wayland to suppress the native DRI3 support.
    Wayland isn't running as a master itself, so it can't do the auth
    on its own and has to ask the compositor to do it for us.  Dropped
    XXX about randr provider -- the conclusion from discussion with
    keithp was that if the driver's dri3_open for a provider on a
    different screen, that's a core dri3 bug.
v3: Don't put quite so much under GLAMOR_NO_DRI3, and add a comment
    explaining what this is about.

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Adam Jackson <ajax@redhat.com>