error[E0658]: no_core is experimental (see issue #29639)
  --> $DIR/cfg-attr-crate-2.rs:15:21
   |
LL | #![cfg_attr(broken, no_core)] //~ ERROR no_core is experimental
   |                     ^^^^^^^^
   |
   = help: add #![feature(no_core)] to the crate attributes to enable

error: aborting due to previous error

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