There is no HW support, but in some cases the shaders mostly work even
if we ignore it, and so far we have just done so. However since the
driver didn't know to what output position in the PVS we should
redirect it, it ended in the first slot. Importantly, if the
CLIP_VERTEX output would be written after position (which actually
belongs in the first slot) it would overwrite it and things blow up.
So just remove it early, and also improve the warning a bit, including
the part that we could use draw module to actually emulate the feature.
Signed-off-by: Pavel Ondračka <pavel.ondracka@gmail.com>
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/11856
Fixes: 5dcef1e7b8
Reviewed-by: Filip Gawin <filip@gawin.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/31547>
cc14d40239