Make the NextScriptId value incrementing method thread-safe, using
CompareAndSwap primitives. This will allow it to be used in the
future for off-thread compilation.

Bug: chromium:1011762
Change-Id: I5b449e75c7dc63d24fa045ae880b0680b54c2f3d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2046883Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66200}