ICE non-eager expansion without a parent scope

When running the following code, the compiler crashes. This bug is reproducible is nightly, beta and stable:

```rust
macro_rules! doc_comment {
    ($x:expr) => {
        #[doc = $x]
        extern {}
    };
}

macro_rules! some_macro {
    ($t1: ty) => {
        doc_comment!{format!("{coor}", coor = stringify!($t1)).as_str()}}
}

fn main() {
    some_macro!(u8);
}
```