This makes sure that the coercion of global import values to numbers
remains non-observable to JavaScript. It allows instantiation failures
to fall back to JavaScript proper without accidentally causing some
side-effect to happen twice. Also coercions might invalidate previous
checks done during linking or throw exceptions.

R=clemensh@chromium.org
TEST=mjsunit/regress/regress-6431
BUG=v8:6431

Change-Id: Ibe2f7a336bc0fb25532d526746ecc802e04bbd5c
Reviewed-on: https://chromium-review.googlesource.com/512544
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46051}