This pooling introduces severe lock contention for Liftoff compilation,
since each compilation uses its own Zone which does at least one
segment allocation.
It's also unclear whether pooling improves performance, since {malloc}
should implement a similar pooling mechanism, but better optimized for
multithreaded uses.

Feel free to revert if this introduces significant regressions.

R=verwaest@chromium.org

Bug: v8:8916
Cq-Include-Trybots: luci.v8.try:v8_linux64_tsan_rel
Change-Id: Iaf988bed898e35700f5f7f3310df8e01918de4c9
Reviewed-on: https://chromium-review.googlesource.com/c/1491632
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59959}