fix a comment to use ASCII aprostrophes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205428 91177308-0d34-0410-b5e6-96231b3b80d8
clarify comment

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@205429 91177308-0d34-0410-b5e6-96231b3b80d8