Enabling once again post-branch point. This CL is expected to come
with major memory improvements and slight performance regressions.

Recent work on performance improvements has focused on x64, hence only
enabling there for now.

Bug: v8:6666
Change-Id: I29dc55eb4e592465073559647e280f74253b73e1
Reviewed-on: https://chromium-review.googlesource.com/1076247
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53544}