Add a default empty string to the 'value' of a string attribute.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175016 91177308-0d34-0410-b5e6-96231b3b80d8
Changed isStoredObjCPointer => IsStoredObjCPointer. No functionality change.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@175017 91177308-0d34-0410-b5e6-96231b3b80d8