[libc++][spaceship] P1614R2: Removed global `operator!=` from `allocator`

[H-G-Hristov]

Summary

Implements parts of P1614R2:

• Removed global operator!= from allocator

[Mordante]

In general LGTM, but I would like to land D152297 first and directly update the status page.

[H-G-Hristov]

Addressed comments

[H-G-Hristov]

In D152612#4411173, @Mordante wrote:

In general LGTM, but I would like to land D152297 first and directly update the status page.

Thank you for the review!

libcxx/include/__memory/allocator.h

268

constexpr since C++20, but removed in C++20. Should I remove the macro?

[Mordante]

Thanks, LGTM after applying your own suggestion.

libcxx/include/__memory/allocator.h

268

Good point, yes please do. We're done the same for the relational operator.

[H-G-Hristov]

Removed macro

libcxx/docs/Status/SpaceshipProjects.csv

 | `nullopt <https://reviews.llvm.org/D146392>`_",None,Hristo Hristov,|Complete|
 "| `[variant.syn] <https://wg21.link/variant.syn>`_
 | `[variant.relops] <https://wg21.link/variant.relops>`_
 | `[variant.monostate.relops] <https://wg21.link/variant.monostate.relops>`_","| `monostate <https://reviews.llvm.org/D131372>`_
 | `variant <https://reviews.llvm.org/D131372>`_",None,Kent Ross,|Complete|
 "| `[template.bitset] <https://wg21.link/template.bitset>`_
 | `[bitset.members] <https://wg21.link/bitset.members>`_","| remove ops `bitset <https://reviews.llvm.org/D152611>`_",None,Hristo Hristov,|Complete|
 | `[memory.syn] <https://wg21.link/memory.syn>`_,|,None,Unassigned,|Not Started|
-| `[allocator.globals] <https://wg21.link/allocator.globals>`_,| remove ops `allocator <https://reviews.llvm.org/D152612>`_,None,Hristo Hristov,|In Progress|
+| `[allocator.globals] <https://wg21.link/allocator.globals>`_,| remove ops `allocator <https://reviews.llvm.org/D152612>`_,None,Hristo Hristov,|Complete|
 | `[unique.ptr.special] <https://wg21.link/unique.ptr.special>`_,| `unique_ptr <https://reviews.llvm.org/D130838>`_,[comparisons.three.way],Adrian Vogelsgesang,|Complete|
 | `[util.smartptr.shared.cmp] <https://wg21.link/util.smartptr.shared.cmp>`_,| `shared_ptr <https://reviews.llvm.org/D130852>`_,[comparisons.three.way],Adrian Vogelsgesang,|Complete|
 "| `[mem.res.syn] <https://wg21.link/mem.res.syn>`_
 | `[mem.res.eq] <https://wg21.link/mem.res.eq>`_
 | `[mem.poly.allocator.eq] <https://wg21.link/mem.poly.allocator.eq>`_","|
 | remove ops `memory_resource <https://reviews.llvm.org/D152629>`_
 | remove ops `polymorphic_allocator <https://reviews.llvm.org/D152629>`_",None,Hristo Hristov,|Complete|
 "| `[allocator.adaptor.syn] <https://wg21.link/allocator.adaptor.syn>`_

libcxx/include/__memory/allocator.h

#if _LIBCPP_STD_VER <= 17 || defined(_LIBCPP_ENABLE_CXX20_REMOVED_ALLOCATOR_MEMBERS)
     }
 #endif
 };
 
 template <class _Tp, class _Up>
 inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
 bool operator==(const allocator<_Tp>&, const allocator<_Up>&) _NOEXCEPT {return true;}
 
+#if _LIBCPP_STD_VER <= 17
+
 template <class _Tp, class _Up>
-inline _LIBCPP_INLINE_VISIBILITY _LIBCPP_CONSTEXPR_SINCE_CXX20
+inline _LIBCPP_INLINE_VISIBILITY
 bool operator!=(const allocator<_Tp>&, const allocator<_Up>&) _NOEXCEPT {return false;}
 
+#endif
+
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___MEMORY_ALLOCATOR_H

libcxx/include/memory

public:
     template <class U>
         void destroy(U* p);                           // deprecated in C++17, removed in C++20
 };
 
 template <class T, class U>
 bool operator==(const allocator<T>&, const allocator<U>&) noexcept; // constexpr in C++20
 
 template <class T, class U>
-bool operator!=(const allocator<T>&, const allocator<U>&) noexcept; // constexpr in C++20
+bool operator!=(const allocator<T>&, const allocator<U>&) noexcept; // removed in C++20
 
 template <class OutputIterator, class T>
 class raw_storage_iterator // deprecated in C++17, removed in C++20
     : public iterator<output_iterator_tag, void, void, void, void> // until C++17
 {
 public:
     typedef output_iterator_tag iterator_category;
     typedef void                value_type;