As is, the DCHECK() has a #if inside, and MSVC has trouble
pre-processing that. Fix this by moving the conditional inside the
DCHECK() into a separate helper function.

Bug: v8:11760
Change-Id: Ib4ae0fe263029bb426da378afa5b6881557ce652
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2919421Reviewed-by: Maya Lekova <mslekova@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74807}