The behaviour was clarified in the spec:
https://github.com/WebAssembly/exception-handling/pull/97

br_on_exn (which was done in another CL) and also rethrow should trap on
nullptr. This CL implements this by an explicit check in the builtin
called for rethrow.

R=jkummerow@chromium.org
CC=aheejin@chromium.org

Bug: v8:10128
Change-Id: Icb0f4e54991b3385917bf183efa825048db4cb82
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2115430
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#66827}