`#![macro_use]` is accepted at crate root

The following code compiles in `lib.rs`.

```rust
#![macro_use]
```

I don't know what it does (hopefully nothing), but it probably shouldn't compile.

cc @JonathanBrouwer @jdonszelmann

### Meta

Reproducible on the playground with version `1.98.0-nightly (2026-05-31 14210df0e27ccd7d9e6a)`