error[E0658]: labels on blocks are unstable
  --> $DIR/feature-gate-label_break_value.rs:2:5
   |
LL |     'a: {
   |     ^^
   |
   = note: see issue #48594 <https://github.com/rust-lang/rust/issues/48594> for more information
   = help: add `#![feature(label_break_value)]` to the crate attributes to enable

error: aborting due to previous error

For more information about this error, try `rustc --explain E0658`.