- Move undef closer to end of usage
- Move I64x2ExtractWithF64x2 closer to Extract tests, and into ifdef
scope so it runs on arm64 builds

Change-Id: I7138c44097975d02e97f4b2b9bfcddd8eb9735c8
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1754544Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63227}