DCHECKs are not really special, they just create a non-constexpr path
within an otherwise constexpr function. Since C++14, this is allowed.
Unfortunately, gcc only supports this since version 6, but we still
need to support gcc 5.

R=ulan@chromium.org

Change-Id: If74486144abafa5bbdcdbb9a567ee9295ac4cfc7
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1862568Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64310}