If background threads are tiering up, they could temporarily make code
writable (if using the mprotect based approach). This would make our
death tests fail (i.e. not crash).
This CL fixes that by repeatedly writing in that case. Eventually, the
code should be protected again, and then we would crash. Failure to
crash would manifest as a timeout of the tests.

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

Bug: v8:11974
Change-Id: Ibe34af499da9b964ad260d58e9b4e390007898e9
Cq-Include-Trybots: luci.v8.try:v8_mac_arm64_rel_ng
Cq-Include-Trybots: luci.v8.try:v8_mac_arm64_dbg_ng
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3151959
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/main@{#76770}