This implements the proper semantics for matching exported/imported
exceptions by using the notion of an "exception tag" that is global to
the system. It can be used to match exceptions in one module against
exceptions declared and/or thrown in another module (or instance).

R=clemensh@chromium.org
TEST=mjsunit/wasm/exceptions-shared
BUG=v8:8091

Change-Id: I37586d7be5d5e6169b3418dfbc415b26dd4750dd
Reviewed-on: https://chromium-review.googlesource.com/1226976
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55940}