[Bug c++/115670] auto return type does not change the linkage for local structs

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=115670

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Simplified case too:
```
auto bar(){
        struct {int i;} t;
        t.i = 0;
    return t;
}
```

This should be local linkage.

Another testcase:
```
namespace {
struct a {int t = 12;};
}
auto bar(){
  struct a t;
    return t;
}
```