[Bug c++/84374] placeholder decltype(auto) accepted when it's not the placeholder alone in trailing-return-type

[smw at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84374

--- Comment #1 from Stephen M. Webb <smw at gcc dot gnu.org> ---
Hrm, evidently the problem is not limited to trailing-return-type declarations,
since the following code also results in no diagnostic.


    decltype(auto)* f();
    class C { decltype(auto)* g(); };

Note though, the problem exists only for function declarations.  An appropriate
diagnostic is issued for other declarations using the placeholder
decltype(auto).