Switching from std::vector to llvm::ArrayRef per post-commit review suggestion.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@216463 91177308-0d34-0410-b5e6-96231b3b80d8
Update for llvm api change.

git-svn-id: http://llvm.org/svn/llvm-project/cfe/trunk@216467 91177308-0d34-0410-b5e6-96231b3b80d8