[openmp] [llvm] [clang] [libcxx] [lld] [mlir] [libc++] Deprecate the _LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_MEMBERS macro (PR #77692)

[Mark de Wever via cfe-commits]

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@@ -117,6 +117,12 @@ Deprecations and Removals
   and ``<experimental/vector>`` have been removed in LLVM 18, as all their contents will have been
   implemented in namespace ``std`` for at least two releases.
 
+- The macro ``_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_MEMBERS`` has been deprecated and will be removed
+  in LLVM 19. This macro used to re-enable redundant members of ``std::allocator<T>`` like ``pointer``,
+  ``reference``, ``rebind``, ``address``, ``max_size``, ``construct``, ``destroy``, and the two-argument
+  overload of ``allocate``. However, this led to the library being non-conforming due to incorrect
+  constexpr-ness. As a result the macro is being deprecated and will be removed in LLVM 19.
----------------
mordante wrote:

The last sentence duplicates the first in this hunk.
```suggestion
  constexpr-ness.
```

https://github.com/llvm/llvm-project/pull/77692