Error on using yield without also using #[coroutine] on the closure

And suggest adding the `#[coroutine]` to the closure

compiler/rustc_middle/src/lib.rs

@@ -35,6 +35,7 @@
 #![feature(const_type_name)]
 #![feature(discriminant_kind)]
 #![feature(coroutines)]
+#![feature(stmt_expr_attributes)]
 #![feature(if_let_guard)]
 #![feature(inline_const)]
 #![feature(iter_from_coroutine)]