Match patterns can't be macros

E.g. 

``` rust
fn main() {
   match &[1,2,3] {
      bytes!("abc") => (),
      _ => ()
   }
}
```

```
pattern-macro.rs:3:11: 3:12 error: expected `=>` but found `!`
pattern-macro.rs:3       bytes!("abc") => (),
                              ^
```

Possibly required for #5346.
