The 'pause' instruction is used for implementing retpolines. It is
currently being printed as 'nop', which is incorrect.

R=titzer@chromium.org

Change-Id: I134b6dae332103fd7f9b3c4e5520f0d5db06ba74
Reviewed-on: https://chromium-review.googlesource.com/1051789Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53109}