Relocate std::endian from <type_traits> to <bit>

This change to an early C++2a feature was just approved (P1612R1).

	* include/std/bit (endian): Move definition here as per P1612R1.
	* include/std/type_traits (endian): Remove definition from here.
	* testsuite/20_util/endian/1.cc: Rename to ...
	* testsuite/26_numerics/endian/1.cc: ... here. Adjust header.

From-SVN: r273816

libstdc++-v3/ChangeLog

+2019-07-25  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/std/bit (endian): Move definition here as per P1612R1.
+	* include/std/type_traits (endian): Remove definition from here.
+	* testsuite/20_util/endian/1.cc: Rename to ...
+	* testsuite/26_numerics/endian/1.cc: ... here. Adjust header.
+
 2019-07-25  Martin Liska  <mliska@suse.cz>
 	    Dominik Infuhr  <dominik.infuehr@theobroma-systems.com>
 

libstdc++-v3/include/std/bit

@@ -315,6 +315,13 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     log2p1(_Tp __x) noexcept
     { return std::__log2p1(__x); }
 
+  /// Byte order
+  enum class endian
+  {
+    little = __ORDER_LITTLE_ENDIAN__,
+    big    = __ORDER_BIG_ENDIAN__,
+    native = __BYTE_ORDER__
+  };
 #endif // C++2a
 
 _GLIBCXX_END_NAMESPACE_VERSION

libstdc++-v3/include/std/type_traits

@@ -3226,14 +3226,6 @@ 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__
-  };
-
   /// Remove references and cv-qualifiers.
   template<typename _Tp>
     struct remove_cvref

libstdc++-v3/testsuite/20_util/endian/1.cc → libstdc++-v3/testsuite/26_numerics/endian/1.cc

@@ -18,7 +18,7 @@
 // { dg-options "-std=gnu++2a" }
 // { dg-do compile { target c++2a } }
 
-#include <type_traits>
+#include <bit>
 
 static_assert( std::is_enum_v<std::endian> );
 static_assert( std::endian::little != std::endian::big );