We were not implementing the specified ToWebAssemblyValue coercion at
all. This caused a failure on arm architectures.

R=ahaas@chromium.org
BUG=v8:5822
TEST=mjsunit/wasm/interpreter

Change-Id: Ic77cfd13007d45308bafa285d517f3820a3b1c80
Reviewed-on: https://chromium-review.googlesource.com/461859
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44185}