This means that targets like pdfium don't have to manually set up the
include dir.

Bug: v8:11292
Change-Id: Idde914592a86f2f5a3fc5cf97060d5650467cc7a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2629280
Commit-Queue: Dan Elphick <delphick@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Dan Elphick <delphick@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72093}