Fix a couple of PPC predefined macros that I spotted while driving by
this code. These aren't technically standard predefines for the platform
but apparantly lots of folks use them as they show up within LLVM's own
codebase. ;] This may even fix some self host issues w/ the JIT!!!

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@184830 91177308-0d34-0410-b5e6-96231b3b80d8