Port 8aeb7439

     Fix for ppc file, using macro functions to xor and add to
     handle the case when kPrimaryMagic/kSecondaryMagic is > 16bits.

R=ishell@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2169183002
Cr-Commit-Position: refs/heads/master@{#37960}