[Bug c++/98939] [C++23] Implement P1787R6 "Declarations and where to find them"

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98939

--- Comment #10 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
```
struct X {
  void foo() const;
  void foo()&&;
};
```

should be allowed with this proposal.