Define std::endian for C++2a (P0463R1)

	* include/std/type_traits (endian): Define new enumeration type.
	* testsuite/20_util/endian/1.cc: New test.

From-SVN: r254381

libstdc++-v3/ChangeLog

 2017-11-03  Jonathan Wakely  <jwakely@redhat.com>
 
+	* include/std/type_traits (endian): Define new enumeration type.
+	* testsuite/20_util/endian/1.cc: New test.
+
 	* include/bits/node_handle.h (_Node_insert_return::get): Remove, as
 	per P0508R0.
 

libstdc++-v3/include/std/type_traits

@@ -2664,7 +2664,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     void operator=(__nonesuch const&) = delete;
   };
 
-#if __cplusplus > 201402L
+#if __cplusplus >= 201703L
 # define __cpp_lib_is_invocable 201703
 
   /// std::invoke_result
@@ -2739,7 +2739,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       = is_nothrow_invocable_r<_Fn, _Args...>::value;
 #endif // C++17
 
-#if __cplusplus > 201402L
+#if __cplusplus >= 201703L
 # define __cpp_lib_type_trait_variable_templates 201510L
 template <typename _Tp>
   inline constexpr bool is_void_v = is_void<_Tp>::value;
@@ -2943,6 +2943,16 @@ template <typename _From, typename _To>
 
 #endif // C++17
 
+#if __cplusplus > 201703L
+  /// Byte order
+  enum class endian
+  {
+    little = __ORDER_LITTLE_ENDIAN__,
+    big    = __ORDER_BIG_ENDIAN__,
+    native = __BYTE_ORDER__
+  };
+#endif // C++2a
+
 _GLIBCXX_END_NAMESPACE_VERSION
 } // namespace std
 

libstdc++-v3/testsuite/20_util/endian/1.cc

+// Copyright (C) 2017 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++2a" }
+// { dg-do compile { target c++2a } }
+
+#include <type_traits>
+
+static_assert( std::is_enum_v<std::endian> );
+static_assert( std::endian::little != std::endian::big );
+static_assert( std::endian::native == std::endian::big
+		|| std::endian::native == std::endian::little );
+
+namespace gnu {
+  int little, big, native;
+}
+
+using namespace std;
+using namespace gnu;
+
+// std::endian is a scoped-enum so these should refer to gnu::native etc.
+int test = little + big + native;