Rollup merge of #152487 - joboet:array_map_zst, r=oli-obk

core: drop unmapped ZSTs in array `map`

Fixes rust-lang/rust#152211.
Alternative to rust-lang/rust#152220 and rust-lang/rust#152248.

This makes the `Drain` type use the same ZST-handling strategy as `slice::IterMut`, which stores the remaining length instead of a one-past-the-end pointer when the type is a ZST. I've also removed the const-generic `N` parameter from `Drain` to avoid unnecessary monomorphizations.

Author: JonathanBrouwer

patches/0027-sysroot_tests-128bit-atomic-operations.patch

@@ -16,6 +16,7 @@ index 1e336bf..35e6f54 100644
 +++ b/coretests/tests/lib.rs
 @@ -2,4 +2,3 @@
  // tidy-alphabetical-start
+ #![cfg_attr(not(panic = "abort"), feature(reentrant_lock))]
 -#![cfg_attr(target_has_atomic = "128", feature(integer_atomics))]
  #![feature(array_ptr_get)]
  #![feature(array_try_from_fn)]
@@ -36,4 +37,3 @@ index b735957..ea728b6 100644
      #[cfg(target_has_atomic = "ptr")]
 --
 2.26.2.7.g19db9cfb68
-