Add allow unstable, fix stability of validity_invariants_of

Author: 5225225

library/core/src/intrinsics.rs

@@ -2151,7 +2151,7 @@ pub struct Invariant {
 /// Returns a list of all validity invariants of the type.
 pub const fn validity_invariants_of<T>() -> &'static [Invariant] {
     extern "rust-intrinsic" {
-        #[rustc_const_stable(feature = "validity_invariants_of", since = "1.40.0")]
+        #[rustc_const_unstable(feature = "validity_invariants_of", issue = "none")]
         pub fn validity_invariants_of<T>() -> &'static [u8];
     }
 

library/core/src/mem/maybe_uninit.rs

@@ -626,6 +626,7 @@ impl<T> MaybeUninit<T> {
     #[inline(always)]
     #[rustc_diagnostic_item = "assume_init"]
     #[track_caller]
+    #[rustc_allow_const_fn_unstable(const_refs_to_cell)]
     pub const unsafe fn assume_init(self) -> T {
         // SAFETY: the caller must guarantee that `self` is initialized.
         // This also means that `self` must be a `value` variant.