As a downside, class-level static variables of FutexEmulation
now have to be local to the .cc file.

Bug: v8:10239
Change-Id: I3d00c65289f346cf2b16fea657f47bff69863b0b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2319989Reviewed-by: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69096}