Attribute macros must be placed before `derive` attributes.

I can't find this anywhere in the reference.

```rust
#[derive(Debug)]
#[my_awesome_macro] // This is an error.
struct S;
```

Currently unstable, see: https://github.com/rust-lang/rust/issues/81119