While the affect values must be valid addresses & thus will not overflow
the IntPtr type, they need to be interpreted as unsigned in comparisons.

Bug: chromium:792549, v8:7123, v8:3590
Change-Id: I864b50c8dbdc297d70bf83c74a83cc466c5f3eb0
Reviewed-on: https://chromium-review.googlesource.com/814395
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49937}