Since C++14, we can use a switch in a constexpr function.

R=ahaas@chromium.org

Bug: v8:9686, v8:9687
Change-Id: I082a7be6c54d6c705b678f19aa56bdb7a3313f80
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1786284Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63596}