In the process:
 - Make it possible to add 'otherwise' labels to operators
 - operators can be defined by non-external macros

Bug: v8:7793
Change-Id: Ia16ae7c95a4719703c80a927dee44c74b65c170b
Reviewed-on: https://chromium-review.googlesource.com/1100826
Commit-Queue: Daniel Clifford <danno@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53754}