Refactor Rc and Arc to use a prefix allocator

library/alloc/src/lib.rs

@@ -76,6 +76,7 @@
 #![cfg_attr(test, feature(test))]
 #![cfg_attr(test, feature(new_uninit))]
 #![feature(allocator_api)]
+#![feature(allocator_api_internals)]
 #![feature(array_chunks)]
 #![feature(array_methods)]
 #![feature(array_windows)]

library/alloc/src/raw_vec.rs

@@ -1,6 +1,8 @@
 #![unstable(feature = "raw_vec_internals", reason = "implementation detail", issue = "none")]
 #![doc(hidden)]
 
+#[cfg(not(no_global_oom_handling))]
+use core::alloc::helper::AllocInit;
 use core::alloc::LayoutError;
 use core::cmp;
 use core::intrinsics;
@@ -18,14 +20,6 @@ use crate::collections::TryReserveError::{self, *};
 #[cfg(test)]
 mod tests;
 
-#[cfg(not(no_global_oom_handling))]
-enum AllocInit {
-    /// The contents of the new memory are uninitialized.
-    Uninitialized,
-    /// The new memory is guaranteed to be zeroed.
-    Zeroed,
-}
-
 /// A low-level utility for more ergonomically allocating, reallocating, and deallocating
 /// a buffer of memory on the heap without having to worry about all the corner cases
 /// involved. This type is excellent for building your own data structures like Vec and VecDeque.