These instructions don't require any work in the emit phase.

Change-Id: I1f82e785afe9a3e3871637349fca3eac3435ab6c
Reviewed-on: https://swiftshader-review.googlesource.com/c/25189Tested-by: Chris Forbes <chrisforbes@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Ben Clayton <bclayton@google.com>