use #[allow(unused_attributes)] to paper over incr.comp problem

Author: Centril

src/libcore/convert.rs

@@ -562,6 +562,7 @@ impl<T> From<T> for T {
 ///
 /// [#64715]: https://github.com/rust-lang/rust/issues/64715
 #[stable(feature = "convert_infallible", since = "1.34.0")]
+#[allow(unused_attributes)]
 #[rustc_reservation_impl = "permitting this impl would forbid us from adding \
                             `impl<T> From<!> for T` later; see rust-lang/rust#64715 for details"]
 impl<T> From<!> for T {