Specify -mcpu=cortex-a15 for krait CPU variants.

Bug: 11178216

Change-Id: I9922e4cd5ba27e3857798aae5c84299e26e054ea
Merge remote-tracking branch 'cyanogen/cm-11.0' into cm-11.0
Merge remote-tracking branch 'cm/cm-11.0' into cm-11.0