This fixes handling of two corner cases with catch-all blocks:
1) The catch-all blocks are conceptually outside the corresponding try.
2) Reachability of catch-all is determined by parent reachability.

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

Change-Id: Idfd8310bc232f3ce389763023c5a33f1ef90e0b5
Reviewed-on: https://chromium-review.googlesource.com/c/1270816Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56486}