Revert "Use a function_ref now that it works (r221753)."

This reverts commit r221756.

David Blaikie pointed out it was unsafe.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221761 91177308-0d34-0410-b5e6-96231b3b80d8
Don't duplicate name in comments. NFC.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221762 91177308-0d34-0410-b5e6-96231b3b80d8
Fix non-variadic function_ref cases to match r221753

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@221763 91177308-0d34-0410-b5e6-96231b3b80d8