[Bug c++/96364] ICE on valid code in cp_finish_decl with auto return type and double attributes

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=96364

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|ICE on valid code in        |ICE on valid code in
                   |cp_finish_decl, at          |cp_finish_decl with auto
                   |cp/decl.c:7537              |return type and double
                   |                            |attributes
           Keywords|                            |rejects-valid

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Full testcase:
```
auto a[[]] [[]]();

auto a() {}
void g()
{
    return a();
}
```

[[]][[]] is causing GCC to think a is a variable decl and not a function decl.
This was even true before Jason's r240756 .

It is even a rejects valid with:
```
void a[[]] [[]]();

void a() {}
void g()
{
    return a();
}
```
Which gives:
```
<source>:2:6: error: variable or field 'a' declared void
    2 | void a[[]] [[]]();
      |      ^
```
and that is not a regression as 4.8.1 even rejects it with that message.