[Bug c++/126149] GCC rejects valid program when auto used in decltype

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=126149

--- Comment #1 from Drea Pinski <pinskia at gcc dot gnu.org> ---
auto has nothing to do with this:
```

struct NoMove {
    NoMove(NoMove&&) = delete;
};

NoMove&& DeclVal();
void     F1(...);
template<class T>
void     F2(T);

using Type1 = decltype(F1(DeclVal()));   // #1: this compiles 
using Type2 = decltype(F2(DeclVal()));   // #2: this doesn't compile when it
should
```

Also is rejected for the same reason ...