This fixes a corner-case where deserialization of a module containing
multiple exported functions of the same signature forgot to properly
unprotect the code-space. Test coverage has been added.

R=clemensh@chromium.org
TEST=mjsunit/wasm/compiled-module-serialization
BUG=chromium:804767

Change-Id: I0082303db19bcc14c4de30f29d604665e281d79d
Reviewed-on: https://chromium-review.googlesource.com/880844Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50799}