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

[jlame646 at gmail dot com via Gcc-bugs]

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

--- Comment #2 from Jason Liam <jlame646 at gmail dot com> ---
Yes, auto was an example. Even replacing `auto` with just NoMove would also
show the problem. 
```
struct NoMove {
    NoMove(NoMove&&) = delete;
};

NoMove&& DeclVal();
void     F1(...);
void     F2(NoMove);

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

```