PR17533 and duplicates: don't compute the return type of an overloaded operator
until after we've referenced the operator; otherwise, we might pick up a
not-yet-deduced type.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@194775 91177308-0d34-0410-b5e6-96231b3b80d8