nir/glsl: Emit memory barriers as part of barrier()

nir/glsl: Emit memory barriers as part of barrier()

The GLSL barrier() intrinsic does an implicit shared memory barrier in
compute shaders and an implicit TCS patch output barrier in tessellation
control shaders.  We'd like NIR's barrier intrinsic to just be a control
flow barrier and not have memory implications.  To satisfy this, we need
to add an extra memory barrier in front of each nir_intrinsic_barrier.

Reviewed-by: Caio Marcelo de Oliveira Filho <caio.oliveira@intel.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3307>