Doesn't show const qualification when using decltype

The following snippet:

```cpp
int main()
{
  const int x = 20;
  decltype(x) y = 30;
}
```

Expands to:

```cpp
int main()
{
  const int x = 20;
  int y = 30;  // should be : const int y
}
```

Where it should be `const int y = 30`;