We were using vqsub incorrectly (which saturates), we need vsub
(wraparound).

Found this issue while running spec test simd_i64x2_arith.js.

Bug: v8:10835
Change-Id: Ic9d45d69e64fa5ff9ddad5de4690f3dd32d1384e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2389100Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69659}