This function is not used (anymore) but needs to be defined, so put an
UNREACHBLE inside.

Bug: v8:7790
Change-Id: I5a8df2cbc236f60ee95ccc9d91c288d8d9c19060
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1515792Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60188}