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

[H-G-Hristov]

Summary

Implements parts of P1614R2

• Removed operator!= from scoped_allocator_adaptor

[H-G-Hristov]

Added revision number

libcxx/docs/Status/SpaceshipProjects.csv

 | `[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>`_
-| `[scoped.adaptor.operators] <https://wg21.link/scoped.adaptor.operators>`_",| remove ops `scoped_allocator_adaptor`,None,Unassigned,|Not Started|
+| `[scoped.adaptor.operators] <https://wg21.link/scoped.adaptor.operators>`_",| remove ops `scoped_allocator_adaptor <https://reviews.llvm.org/D152678>`_,None,Hristo Hristov,|Complete|
 "| `[functional.syn] <https://wg21.link/functional.syn>`_
 | `[range.cmp] <https://wg21.link/range.cmp>`_
 | `[func.wrap.func] <https://wg21.link/func.wrap.func>`_
 | `[func.wrap.func.nullptr] <https://wg21.link/func.wrap.func.nullptr>`_",| remove ops `function`,None,Unassigned,|Not Started|
 | `[meta.unary.prop] <https://wg21.link/meta.unary.prop>`_,| replaced by `issue LWG3354 <https://wg21.link/LWG3354>`_,None,Unassigned,|Nothing To Do|
 | `[meta.trans.other] <https://wg21.link/meta.trans.other>`_,|,None,Unassigned,|Not Started|
 "| `[type.index.overview] <https://wg21.link/type.index.overview>`_
 | `[type.index.members] <https://wg21.link/type.index.members>`_",| `type_index <https://reviews.llvm.org/D131357>`_,None,Adrian Vogelsgesang,|Complete|

libcxx/include/scoped_allocator

 template <class OuterA1, class OuterA2, class... InnerAllocs>
     bool
     operator==(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
                const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b) noexcept;
 
 template <class OuterA1, class OuterA2, class... InnerAllocs>
     bool
     operator!=(const scoped_allocator_adaptor<OuterA1, InnerAllocs...>& a,
-               const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b) noexcept;
+               const scoped_allocator_adaptor<OuterA2, InnerAllocs...>& b) noexcept; // removed in C++20
 
 }  // std
 
 */
 
 #include <__assert> // all public C++ headers provide the assertion handler
 #include <__config>
 #include <__memory/allocator_traits.h>

 bool
 operator==(const scoped_allocator_adaptor<_OuterA1, _InnerA0, _InnerAllocs...>& __a,
            const scoped_allocator_adaptor<_OuterA2, _InnerA0, _InnerAllocs...>& __b) _NOEXCEPT
 {
     return __a.outer_allocator() == __b.outer_allocator() &&
            __a.inner_allocator() == __b.inner_allocator();
 }
 
+#if _LIBCPP_STD_VER <= 17
+
 template <class _OuterA1, class _OuterA2, class... _InnerAllocs>
 inline _LIBCPP_INLINE_VISIBILITY
 bool
 operator!=(const scoped_allocator_adaptor<_OuterA1, _InnerAllocs...>& __a,
            const scoped_allocator_adaptor<_OuterA2, _InnerAllocs...>& __b) _NOEXCEPT
 {
     return !(__a == __b);
 }
 
+#endif // _LIBCPP_STD_VER <= 17
+
 #endif // !defined(_LIBCPP_CXX03_LANG)
 
 _LIBCPP_END_NAMESPACE_STD
 
 #if !defined(_LIBCPP_REMOVE_TRANSITIVE_INCLUDES) && _LIBCPP_STD_VER <= 20
 #  include <atomic>
 #  include <climits>
 #  include <concepts>