As the comment notes, we want to ensure that code space is *not*
writable by the current thread.

R=jkummerow@chromium.org
CC=mpdenton@chromium.org

Bug: v8:11974
Change-Id: I5c3cad32b8edc56013f298405c8e20d8bc9da05f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3173675Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76985}