It's deprecated in C++17 and not needed (it was needed for static const,
but not for constexpr). It's needed in C++14, but can trigger
deprecation errors in C++17, so include it conditionally on __cplusplus.

Bug: chromium:1274247
Change-Id: I92524f377bb92ac2aa008f15830920786a1c1432
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3308795
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78157}