error[E0658]: C-variadic functions with the "system" calling convention are unstable
  --> $DIR/feature-gate-extern_system_varargs.rs:1:14
   |
LL | fn system(f: extern "system" fn(usize, ...)) {
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: see issue #136946 <https://github.com/rust-lang/rust/issues/136946> for more information
   = help: add `#![feature(extern_system_varargs)]` to the crate attributes to enable
   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date

error: aborting due to 1 previous error

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