enhanced layout support.
The enhanced layout extension allows for gaps in the streamout bindings so we have to be able to handle no-handles in the middle of the target array.
TGSI also has to deal with components outputs where multiple outputs can be mentioned in the TGSI. It's safe for use to just skip the extra outputs at least for the tests I've been able to run.
Once we have those changes in place, the renderer can expose the new CAP bit to the host without any further host extension checks.
Mesa patch: https://gitlab.freedesktop.org/airlied/mesa/commits/virgl-enhanced_layouts