This adds support for i32.wrap/i64, i64.extend_s/i32, and
i64.extend_u/i32.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: Iaeac1d24a53d044151cb244fffe3eab04314d908
Reviewed-on: https://chromium-review.googlesource.com/962281
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51930}