This change allows the PPC simulator to execute on PPC hardware where,
due to calling conventions, we must distinguish between Object* and
ObjectPair return values.

We find this useful as another available option for debugging certain
problems.  While not strictly necessary for Intel platforms, we hope
that this is less offensive now that BUILTIN_CALL_TRIPLE has been
added.

BUG=
R=rmcilroy@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com

Review URL: https://codereview.chromium.org/1604653006

Cr-Commit-Position: refs/heads/master@{#33475}