This makes the bitcasts that change pointerness effectful so that
they are not accidentally reordered with memory allocation.

Change-Id: I70e820fc0de1adb2a81b52a43bce4d47f2c304b9
Reviewed-on: https://chromium-review.googlesource.com/852052Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Jaroslav Sevcik <jarin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50374}