rework the remaining autoupgrade logic to use a StringRef instead of creating a

rework the remaining autoupgrade logic to use a StringRef instead of creating a
temporary std::string for every function being checked.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@133355 91177308-0d34-0410-b5e6-96231b3b80d8