When generating the code for an illegal (non-js-compliant) wrapper for
a js function, we were generating a zero constant of the return type.
This failed on ia32 if the return type is i64.
The correct thing to do is to return two i32 zero constants.

R=titzer@chromium.org
BUG=v8:6104, v8:6096

Change-Id: Idc0dd8d3eef901c22d5278d97f1879b000a18588
Reviewed-on: https://chromium-review.googlesource.com/455857Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43835}