allow internal_features, added in https://github.com/rust-lang/rust/pull/108955

library/compiler-builtins/examples/intrinsics.rs

@@ -5,6 +5,7 @@
 
 #![allow(unused_features)]
 #![allow(stable_features)] // bench_black_box feature is stable, leaving for backcompat
+#![allow(internal_features)]
 #![cfg_attr(thumb, no_main)]
 #![deny(dead_code)]
 #![feature(bench_black_box)]

library/compiler-builtins/src/lib.rs

@@ -14,6 +14,7 @@
 #![no_builtins]
 #![no_std]
 #![allow(unused_features)]
+#![allow(internal_features)]
 // We use `u128` in a whole bunch of places which we currently agree with the
 // compiler on ABIs and such, so we should be "good enough" for now and changes
 // to the `u128` ABI will be reflected here.