error[E0658]: repr with 128-bit type is unstable
  --> $DIR/E0658.rs:2:1
   |
LL | enum Foo {
   | ^^^^^^^^
   |
   = note: see issue #56071 <https://github.com/rust-lang/rust/issues/56071> for more information
   = help: add `#![feature(repr128)]` 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   = note: this compiler was built on YYYY-MM-DD; consider upgrading it if it is out of date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`.