The following code compiles with GCC and MSVC but fails with clang

```
namespace a {
template <typename> class b {
  public:
  typedef int string_type;
  operator string_type();
};
} // namespace a
template <class> void c() {
    &a::b<char>::operator string_type; 
}
```

Godbolt - https://godbolt.org/z/sWs8rvq98

Clang accepts the code if `string_type` is qualified - https://godbolt.org/z/efPd9d8Gz . Based on examples in http://eel.is/c++draft/basic.lookup#unqual-5, I think the lookup should succeed without qualification as well. 
[Clang] Bug with lookup
This is a GitHub Issue
repo:llvm-project
owner:llvm
Title : [Clang] Bug with lookup
Issue date:

--- start body ---
The following code compiles with GCC and MSVC but fails with clang

```
namespace a {
template <typename> class b {
  public:
  typedef int string_type;
  operator string_type();
};
} // namespace a
template <class> void c() {
    &a::b<char>::operator string_type; 
}
```

Godbolt - https://godbolt.org/z/sWs8rvq98

Clang accepts the code if `string_type` is qualified - https://godbolt.org/z/efPd9d8Gz . Based on examples in http://eel.is/c++draft/basic.lookup#unqual-5, I think the lookup should succeed without qualification as well. 
--- end body ---
