The helper encapsulates the `x - x` pattern to silence NaN `x`.

Bug: v8:7519
Change-Id: Ia633272d7b7cc350c7e4db07e271e0192c68019f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2637232
Auto-Submit: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Nico Hartmann <nicohartmann@chromium.org>
Reviewed-by: Nico Hartmann <nicohartmann@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72161}