Labeled break outside of breakable frames says break cannot be used outside of a loop

[nagisa]

fn main() {
    break 'foo;
}

Will output the following diagnostics:

error[E0426]: use of undeclared label `'foo`
 --> src/main.rs:2:11
  |
2 |     break 'foo;
  |           ^^^^ undeclared label `'foo`

error[E0268]: `break` outside of a loop
 --> src/main.rs:2:5
  |
2 |     break 'foo;
  |     ^^^^^^^^^^ cannot `break` outside of a loop

With break now supported in conjunction with non-loop constructs, we should adjust this diagnostic accordingly. The wording here might be tricky, because something like

cannot break outside of a loop or a labeled block

would go stale as soon as we add another thing/place you can break out of, and the wording in general reads awkward regardless...

[compiler-errors]

(just my 2¢, but I actually think "cannot break outside of a loop or labeled block" is totally fine for now.)