gallivm: Fix handling of nir_intrinsic_scoped_barrier

A scoped barrier only has a control barrier behavior if there's
an execution scope.

Fixes: 13d900de0dcf ("llvmpipe: set nir_shader_compiler_options::use_scoped_barrier")
Reviewed-by: Faith Ekstrand <faith.ekstrand@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3339>
(cherry picked from commit 2178a8da51fee6dc266541c468de58e66b7b0e17)
2 files changed