error[E0658]: a `#[start]` function is an experimental feature whose signature may change over time
  --> $DIR/feature-gate-start.rs:2:1
   |
LL | fn foo(_: isize, _: *const *const u8) -> isize { 0 }
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: for more information, see https://github.com/rust-lang/rust/issues/29633
   = help: add `#![feature(start)]` to the crate attributes to enable

error: aborting due to previous error

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