E0518 needs to be updated to new format

[sophiajt]

From: src/test/compile-fail/E0518.rs

E0518 needs a span_label, updating it from:

error[E0518]: attribute should be applied to function
  --> src/test/compile-fail/E0518.rs:11:1
   |
11 | #[inline(always)] //~ ERROR E0518
   | ^^^^^^^^^^^^^^^^^

To:

error[E0518]: attribute should be applied to function
  --> src/test/compile-fail/E0518.rs:11:1
   |
11 | #[inline(always)] //~ ERROR E0518
   | ^^^^^^^^^^^^^^^^^ requires a function