1) Ensure 31bit Smis are enabled if pointer compression is.
2) Enable some code for 31bit Smis

Bug: v8:8344
Change-Id: Ib1e68ebfcfd49e16d1548879b7670c88dc73449b
Reviewed-on: https://chromium-review.googlesource.com/c/1445979
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59248}