Guard band clipping speeds up rasterization for primitives that are partially off-screen. This change in particular results in small framerate improvements in a wide range of games. Started by Grigori Goronzy <greg@chown.ath.cx>. Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com> Reviewed-by: Grigori Goronzy <greg@chown.ath.cx> Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>