x64 code path is different and we can't do this optimization.

Bug: v8:9771
Change-Id: I1639e53b4397873e70895ec2919ac2769b0bbc72
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1826728Reviewed-by: Dan Elphick <delphick@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64022}