Use llvm::makeArrayRef instead of explicitly calling ArrayRef constructor and mentioning the type. This works now that we have a conversion from ArrayRef<T*> to ArrayRef<const T*>.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@216824 91177308-0d34-0410-b5e6-96231b3b80d8
Fix some cases where StringRef was being passed by const reference. Remove const from some other StringRefs since its implicitly const already.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@216825 91177308-0d34-0410-b5e6-96231b3b80d8