Gallium drivers should never see nir_var_uniform because gallium lowers
regular uniforms to a UBO. No GL driver should ever see either
nir_var_mem_shared because that's lowered in GLSL IR.
Reviewed-by: Eric Anholt <eric@anholt.net> Reviewed-by: Connor Abbott <cwabbott0@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5418>