A stability attribute has been used outside of the standard library.

Erroneous code example:

```compile_fail,E0734
#[rustc_deprecated(since = "b", reason = "text")] // invalid
#[stable(feature = "a", since = "b")] // invalid
#[unstable(feature = "b", issue = "none")] // invalid
fn foo(){}
```

These attributes are meant to only be used by the standard library and are
rejected in your own crates.
