libstdc++: Add comparison operators to associative containers

The last C++20 changes from P1614R2, "The Mothership has Landed"

	* include/bits/stl_map.h (map): Define operator<=> and remove
	operator< for C++20.
	* include/bits/stl_multimap.h (multimap): Likewise.
	* include/bits/stl_multiset.h (multiset): Likewise.
	* include/bits/stl_set.h (set): Likewise.
	* include/bits/stl_tree.h (_Rb_tree): Likewise.
	(_Rb_tree_iterator, _Rb_tree_const_iterator): Remove redundant
	operator!= for C++20.
	* include/debug/map.h (__gnu_debug::map): Define operator<=> for C++20.
	* include/debug/multimap.h (__gnu_debug::multimap): Likewise.
	* include/debug/multiset.h (__gnu_debug::multiset): Likewise.
	* include/debug/set.h (__gnu_debug::set): Likewise.
	* testsuite/23_containers/map/operators/cmp_c++20.cc: New test.
	* testsuite/23_containers/multimap/operators/cmp_c++20.cc: New test.
	* testsuite/23_containers/multiset/operators/cmp_c++20.cc: New test.
	* testsuite/23_containers/set/operators/cmp_c++20.cc: New test.

4 files changed, 35 insertions, 3 deletions

diff --git a/libstdc++-v3/include/debug/map.h b/libstdc++-v3/include/debug/map.h
index e96fc31f522..adbabf62915 100644
--- a/libstdc++-v3/include/debug/map.h
+++ b/libstdc++-v3/include/debug/map.h
@@ -731,7 +731,7 @@ namespace __debug
     map(initializer_list<pair<_Key, _Tp>>, _Allocator)
     -> map<_Key, _Tp, less<_Key>, _Allocator>;
 
-#endif
+#endif // deduction guides
 
   template<typename _Key, typename _Tp,
 	   typename _Compare, typename _Allocator>
@@ -740,6 +740,13 @@ namespace __debug
 	       const map<_Key, _Tp, _Compare, _Allocator>& __rhs)
     { return __lhs._M_base() == __rhs._M_base(); }
 
+#if __cpp_lib_three_way_comparison
+  template<typename _Key, typename _Tp, typename _Compare, typename _Alloc>
+    inline __detail::__synth3way_t<pair<const _Key, _Tp>>
+    operator<=>(const map<_Key, _Tp, _Compare, _Alloc>& __lhs,
+		const map<_Key, _Tp, _Compare, _Alloc>& __rhs)
+    { return __lhs._M_base() <=> __rhs._M_base(); }
+#else
   template<typename _Key, typename _Tp,
 	   typename _Compare, typename _Allocator>
     inline bool
@@ -774,6 +781,7 @@ namespace __debug
     operator>(const map<_Key, _Tp, _Compare, _Allocator>& __lhs,
 	      const map<_Key, _Tp, _Compare, _Allocator>& __rhs)
     { return __lhs._M_base() > __rhs._M_base(); }
+#endif // three-way comparison
 
   template<typename _Key, typename _Tp,
 	   typename _Compare, typename _Allocator>
diff --git a/libstdc++-v3/include/debug/multimap.h b/libstdc++-v3/include/debug/multimap.h
index 83de49e87e2..6cba52d35dc 100644
--- a/libstdc++-v3/include/debug/multimap.h
+++ b/libstdc++-v3/include/debug/multimap.h
@@ -621,6 +621,13 @@ namespace __debug
 	       const multimap<_Key, _Tp, _Compare, _Allocator>& __rhs)
     { return __lhs._M_base() == __rhs._M_base(); }
 
+#if __cpp_lib_three_way_comparison
+  template<typename _Key, typename _Tp, typename _Compare, typename _Alloc>
+    inline __detail::__synth3way_t<pair<const _Key, _Tp>>
+    operator<=>(const multimap<_Key, _Tp, _Compare, _Alloc>& __lhs,
+		const multimap<_Key, _Tp, _Compare, _Alloc>& __rhs)
+    { return __lhs._M_base() <=> __rhs._M_base(); }
+#else
   template<typename _Key, typename _Tp,
 	   typename _Compare, typename _Allocator>
     inline bool
@@ -655,6 +662,7 @@ namespace __debug
     operator>(const multimap<_Key, _Tp, _Compare, _Allocator>& __lhs,
 	      const multimap<_Key, _Tp, _Compare, _Allocator>& __rhs)
     { return __lhs._M_base() > __rhs._M_base(); }
+#endif // three-way comparison
 
   template<typename _Key, typename _Tp,
 	   typename _Compare, typename _Allocator>
diff --git a/libstdc++-v3/include/debug/multiset.h b/libstdc++-v3/include/debug/multiset.h
index fcbba339478..a2d5e717b34 100644
--- a/libstdc++-v3/include/debug/multiset.h
+++ b/libstdc++-v3/include/debug/multiset.h
@@ -584,7 +584,7 @@ namespace __debug
     multiset(initializer_list<_Key>, _Allocator)
     -> multiset<_Key, less<_Key>, _Allocator>;
 
-#endif
+#endif // deduction guides
 
   template<typename _Key, typename _Compare, typename _Allocator>
     inline bool
@@ -592,6 +592,13 @@ namespace __debug
 	       const multiset<_Key, _Compare, _Allocator>& __rhs)
     { return __lhs._M_base() == __rhs._M_base(); }
 
+#if __cpp_lib_three_way_comparison
+  template<typename _Key, typename _Compare, typename _Alloc>
+    inline __detail::__synth3way_t<_Key>
+    operator<=>(const multiset<_Key, _Compare, _Alloc>& __lhs,
+		const multiset<_Key, _Compare, _Alloc>& __rhs)
+    { return __lhs._M_base() <=> __rhs._M_base(); }
+#else
   template<typename _Key, typename _Compare, typename _Allocator>
     inline bool
     operator!=(const multiset<_Key, _Compare, _Allocator>& __lhs,
@@ -621,6 +628,7 @@ namespace __debug
     operator>(const multiset<_Key, _Compare, _Allocator>& __lhs,
 	      const multiset<_Key, _Compare, _Allocator>& __rhs)
     { return __lhs._M_base() > __rhs._M_base(); }
+#endif // three-way comparison
 
   template<typename _Key, typename _Compare, typename _Allocator>
     void
diff --git a/libstdc++-v3/include/debug/set.h b/libstdc++-v3/include/debug/set.h
index 093ff129f3e..210186623df 100644
--- a/libstdc++-v3/include/debug/set.h
+++ b/libstdc++-v3/include/debug/set.h
@@ -595,7 +595,7 @@ namespace __debug
     set(initializer_list<_Key>, _Allocator)
     -> set<_Key, less<_Key>, _Allocator>;
 
-#endif
+#endif // deduction guides
 
   template<typename _Key, typename _Compare, typename _Allocator>
     inline bool
@@ -603,6 +603,13 @@ namespace __debug
 	       const set<_Key, _Compare, _Allocator>& __rhs)
     { return __lhs._M_base() == __rhs._M_base(); }
 
+#if __cpp_lib_three_way_comparison
+  template<typename _Key, typename _Compare, typename _Alloc>
+    inline __detail::__synth3way_t<_Key>
+    operator<=>(const set<_Key, _Compare, _Alloc>& __lhs,
+		const set<_Key, _Compare, _Alloc>& __rhs)
+    { return __lhs._M_base() <=> __rhs._M_base(); }
+#else
   template<typename _Key, typename _Compare, typename _Allocator>
     inline bool
     operator!=(const set<_Key, _Compare, _Allocator>& __lhs,
@@ -632,6 +639,7 @@ namespace __debug
     operator>(const set<_Key, _Compare, _Allocator>& __lhs,
 	      const set<_Key, _Compare, _Allocator>& __rhs)
     { return __lhs._M_base() > __rhs._M_base(); }
+#endif // three-way comparison
 
   template<typename _Key, typename _Compare, typename _Allocator>
     void