Fix English grammar error.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184463 91177308-0d34-0410-b5e6-96231b3b80d8
Add test.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184465 91177308-0d34-0410-b5e6-96231b3b80d8
Clean up warning and add a test.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@184466 91177308-0d34-0410-b5e6-96231b3b80d8