This makes sure that catch blocks that are practically unreachable due
to missing exceptional projections are handled properly. Note that this
is independent of how reachability will be outlined in the final spec
for exception handling. Currently we just assume that all catch blocks
are spec-wise reachable.

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

Change-Id: I13607a59bd76be146df836e88105a2fbafedb760
Reviewed-on: https://chromium-review.googlesource.com/c/1273018Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56556}