The various compilation caches are tricky to understand. Hopefully
some addtl. documentation helps.

Bug: v8:8888
Change-Id: I20f2778b5548fcc38724aca600ccf770c240758d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2516476
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70966}