crtdbg.h provides the declarations for _CrtSetReportMode and the _CRT_*
constants. It should have moved in
https://chromium-review.googlesource.com/968244, but the MSVC C++
headers appear to include crtdbg.h transitively, so we only noticed this
on the libc++ Windows buildbot.

Tbr: mlippautz@chromium.org
Bug: chromium:801780
Change-Id: Ia07f6136e4b8d1f25014e00b0b9f662029ab5a2b
Reviewed-on: https://chromium-review.googlesource.com/981399
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52309}