Use ArrayRef in some function parameters instead of a pointer and count. No functional change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210750 91177308-0d34-0410-b5e6-96231b3b80d8
Use StringRef to simplify code. No functional change.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@210751 91177308-0d34-0410-b5e6-96231b3b80d8