This is a reland of dacce720

Original change's description:
> [wasm] Fix fallback from PKU to mprotect
>
> The {WasmCodeManager::SetThreadWritable} method would return true if
> called in a nested scope, even if PKU is not available. The caller
> cannot tell then whether permission switching happened or not.
>
> This CL refactors the code to do an explicit check for PKU support, and
> removes the boolean return value from {SetThreadWritable}.
>
> R=jkummerow@chromium.org
>
> Bug: v8:11959, v8:11974
> Change-Id: I2d45f1fa240305c6f92f63cdf190131d637bfe95
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3021383
> Commit-Queue: Clemens Backes <clemensb@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#75699}

Bug: v8:11959, v8:11974
Change-Id: I7086aa3f1cd12615e6f12bbd061084ecd325eb11
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3021180Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#75707}