This adds support for i64.eqz, and all binary comparisons (i64.eq,
i64.ne, i64.lt_s, i64.le_s, i64.lt_u, i64.le_u, i64.gt_s, i64.ge_s,
i64.gt_u, i64.and i64.ge_u).

R=titzer@chromium.org

Bug: v8:6600
Change-Id: Ic6c59529b007220698e09d5959394bcfb6590173
Reviewed-on: https://chromium-review.googlesource.com/969125
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52063}