Introduced in https://crrev.com/c/2250243.

CONSTEXPR_DCHECK(cond) replaces the longer

 #if V8_HAS_CXX14_CONSTEXPR
     DCHECK(cond);
 #endif

pattern.

Change-Id: I636e5b4b40bffb29b2e82c81285b2ef78a822745
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2250244Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68402}