Simplify expression, made possible by r199702.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199703 91177308-0d34-0410-b5e6-96231b3b80d8
Now that r199688 avoids the real issue, use private linkage for objc strings.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199705 91177308-0d34-0410-b5e6-96231b3b80d8