Address #2281


```
-> % cat foo.rs
fn foo() -> int {
    let bar = 10;

    bad
}
```

```
-> % rustc foo.rs
foo.rs:4:4: 4:7 error: unresolved name: `bad`. Did you mean: `bar`?
foo.rs:4     bad
             ^~~
error: aborting due to previous error
```

Don't use ExpnKind::descr to get the name of a bang macro.

This is the same change as the first commit in rust-lang#68407, but applied to clippy.
The new code should work both before and after the changes in rust-lang#68407.

changelog: none

fix spurious epoll-blocking test