This implements AssertUnreachable for the arm32 port of Liftoff.

Bug: v8:6600
Change-Id: I9aa5083dc1be175fc5f2f386d8aace021bab3b03
Reviewed-on: https://chromium-review.googlesource.com/c/1346335
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57767}