It reflects the semantics of ToBoolean, so it must be adapted for
bigints.

Bug: v8:6791
Change-Id: I18931df21528463dacf5ad50fa8264b1c968c6b5
Reviewed-on: https://chromium-review.googlesource.com/799831Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49776}