We already have specialized logic for unops and binops, and the generic
{BuildSimpleOperator} implementation (based on a signature) was
reimplementing these two cases.
This CL avoids the switch since we only need to handle exactly two
cases, and redirects to the existing methods for implementing them.

R=thibaudm@chromium.org

Bug: v8:10576
Change-Id: I8eb5c768f0fa59e48503c108498b334a0ae9037a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2249859Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68456}