stabilize the intrinsic

Author: bend-n

Diff for: library/core/src/intrinsics/mod.rs

@@ -3675,6 +3675,7 @@ pub const unsafe fn ptr_offset_from<T>(_ptr: *const T, _base: *const T) -> isize
 #[rustc_nounwind]
 #[rustc_intrinsic]
 #[rustc_intrinsic_must_be_overridden]
+#[rustc_intrinsic_const_stable_indirect]
 pub const unsafe fn ptr_offset_from_unsigned<T>(_ptr: *const T, _base: *const T) -> usize {
     unimplemented!()
 }

Diff for: library/core/src/ptr/const_ptr.rs

@@ -766,7 +766,6 @@ impl<T: ?Sized> *const T {
     /// ```
     #[stable(feature = "ptr_sub_ptr", since = "CURRENT_RUSTC_VERSION")]
     #[rustc_const_stable(feature = "const_ptr_sub_ptr", since = "CURRENT_RUSTC_VERSION")]
-    #[rustc_allow_const_fn_unstable(core_intrinsics)]
     #[inline]
     #[cfg_attr(miri, track_caller)] // even without panics, this helps for Miri backtraces
     pub const unsafe fn sub_ptr(self, origin: *const T) -> usize