libstdc++: Define <=> for Debug Mode array

This fixes a test failure with -D_GLIBCXX_DEBUG:

FAIL: 23_containers/array/comparison_operators/constexpr.cc (test for excess errors)

	* include/debug/array (operator<=>): Define for C++20.
	* testsuite/23_containers/array/tuple_interface/get_debug_neg.cc:
	Adjust dg-error line numbers.
	* testsuite/23_containers/array/tuple_interface/
	tuple_element_debug_neg.cc: Likewise.

libstdc++-v3/ChangeLog

 2020-02-27  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/debug/array (operator<=>): Define for C++20.
+	* testsuite/23_containers/array/tuple_interface/get_debug_neg.cc:
+	Adjust dg-error line numbers.
+	* testsuite/23_containers/array/tuple_interface/
+	tuple_element_debug_neg.cc: Likewise.
+
 	* testsuite/23_containers/span/back_assert_neg.cc: Add #undef before
 	defining _GLIBCXX_ASSERTIONS.
 	* testsuite/23_containers/span/first_2_assert_neg.cc: Likewise.

libstdc++-v3/include/debug/array

@@ -239,6 +239,25 @@ namespace __debug
     operator==(const array<_Tp, _Nm>& __one, const array<_Tp, _Nm>& __two)
     { return std::equal(__one.begin(), __one.end(), __two.begin()); }
 
+#if __cpp_lib_three_way_comparison && __cpp_lib_concepts
+  template<typename _Tp, size_t _Nm>
+    constexpr __detail::__synth3way_t<_Tp>
+    operator<=>(const array<_Tp, _Nm>& __a, const array<_Tp, _Nm>& __b)
+    {
+      if constexpr (_Nm && __is_byte<_Tp>::__value)
+	return __builtin_memcmp(__a.data(), __b.data(), _Nm) <=> 0;
+      else
+	{
+	  for (size_t __i = 0; __i < _Nm; ++__i)
+	    {
+	      auto __c = __detail::__synth3way(__a[__i], __b[__i]);
+	      if (__c != 0)
+		return __c;
+	    }
+	}
+      return strong_ordering::equal;
+    }
+#else
   template<typename _Tp, std::size_t _Nm>
     _GLIBCXX20_CONSTEXPR
     inline bool
@@ -271,6 +290,7 @@ namespace __debug
     inline bool
     operator>=(const array<_Tp, _Nm>& __one, const array<_Tp, _Nm>& __two)
     { return !(__one < __two); }
+#endif // three_way_comparison && concepts
 
   // Specialized algorithms.
 

libstdc++-v3/testsuite/23_containers/array/tuple_interface/get_debug_neg.cc

@@ -27,6 +27,6 @@ int n1 = std::get<1>(a);
 int n2 = std::get<1>(std::move(a));
 int n3 = std::get<1>(ca);
 
-// { dg-error "static assertion failed" "" { target *-*-* } 295 }
-// { dg-error "static assertion failed" "" { target *-*-* } 304 }
-// { dg-error "static assertion failed" "" { target *-*-* } 312 }
+// { dg-error "static assertion failed" "" { target *-*-* } 315 }
+// { dg-error "static assertion failed" "" { target *-*-* } 324 }
+// { dg-error "static assertion failed" "" { target *-*-* } 332 }

libstdc++-v3/testsuite/23_containers/array/tuple_interface/tuple_element_debug_neg.cc

@@ -22,4 +22,4 @@
 
 typedef std::tuple_element<1, std::array<int, 1>>::type type;
 
-// { dg-error "static assertion failed" "" { target *-*-* } 377 }
+// { dg-error "static assertion failed" "" { target *-*-* } 397 }