Navi 10 can hang when an NGG workgroup has no output,
so we work around that by always exporting a single zero-area
triangle with a single vertex that has all-NaN coordinates.
Thus far, we only employed this for NGG GS, because on all
other stages, the output can't be empty.
However, with NGG culling, the output can be empty, so let's
apply the same workaround there too.
Cc: mesa-stable
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Rhys Perry <pendingchaos02@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/12169>
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