[Bug c++/120335] Defining a function return type allowed with -pedantic-errors with using statement

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120335

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Testcase:
```
using T = struct {}();
```