Stabilize const_raw_ptr_deref for *const T

This stabilizes dereferencing immutable raw pointers in const contexts.
It does not stabilize `*mut T` dereferencing. This is placed behind the
`const_raw_mut_ptr_deref` feature gate.

Author: jhpratt

core/src/lib.rs

@@ -156,7 +156,7 @@
 #![feature(const_impl_trait)]
 #![feature(const_mut_refs)]
 #![feature(const_precise_live_drops)]
-#![feature(const_raw_ptr_deref)]
+#![cfg_attr(bootstrap, feature(const_raw_ptr_deref))]
 #![feature(const_refs_to_cell)]
 #![feature(decl_macro)]
 #![feature(doc_cfg)]

core/tests/lib.rs

@@ -56,7 +56,7 @@
 #![feature(const_mut_refs)]
 #![feature(const_pin)]
 #![feature(const_slice_from_raw_parts)]
-#![feature(const_raw_ptr_deref)]
+#![cfg_attr(bootstrap, feature(const_raw_ptr_deref))]
 #![feature(never_type)]
 #![feature(unwrap_infallible)]
 #![feature(result_into_ok_or_err)]

std/src/lib.rs

@@ -264,7 +264,8 @@
 #![feature(const_ipv4)]
 #![feature(const_ipv6)]
 #![feature(const_option)]
-#![feature(const_raw_ptr_deref)]
+#![cfg_attr(bootstrap, feature(const_raw_ptr_deref))]
+#![cfg_attr(not(bootstrap), feature(const_mut_refs))]
 #![feature(const_socketaddr)]
 #![feature(const_trait_impl)]
 #![feature(container_error_extra)]