error[E0658]: the `#[default_lib_allocator]` attribute is an experimental feature
  --> $DIR/feature-gate-allocator_internals.rs:1:1
   |
LL | #![default_lib_allocator]
   | ^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: add `#![feature(allocator_internals)]` to the crate attributes to enable

error: aborting due to previous error

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