llvmpipe: enable ARB_gpu_shader5

This isn't fully free of bugs, but it's good to get CI working,
so fixing those bugs doesn't break anything.

The main buggy areas are missing indirect texture size,
and transform feedback geometry streams.

Reviewed-by: Roland Scheidegger <sroland@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3778>
6 files changed