Add a feature macro for C++17 make_from_tuple.

	* include/std/tuple (__cpp_lib_make_from_tuple): New.
	* testsuite/20_util/tuple/make_from_tuple/1.cc: Adjust.

From-SVN: r239480

libstdc++-v3/ChangeLog

+2016-08-15  Ville Voutilainen  <ville.voutilainen@gmail.com>
+
+	Add a feature macro for C++17 make_from_tuple.
+	* include/std/tuple (__cpp_lib_make_from_tuple): New.
+	(__make_from_tuple_impl(_Tuple&&, index_sequence<_Idx...>)):
+	Qualify the call to get<>().
+	* testsuite/20_util/tuple/make_from_tuple/1.cc: Adjust.
+
 2016-08-15  Uros Bizjak  <ubizjak@gmail.com>
 
 	* src/filesystem/ops.cc: Always include ostream and

libstdc++-v3/include/std/tuple

@@ -1656,10 +1656,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 			  _Indices{});
     }
 
+#define __cpp_lib_make_from_tuple  201606
+
   template <typename _Tp, typename _Tuple, size_t... _Idx>
     constexpr _Tp
     __make_from_tuple_impl(_Tuple&& __t, index_sequence<_Idx...>)
-    { return _Tp(get<_Idx>(std::forward<_Tuple>(__t))...); }
+    { return _Tp(std::get<_Idx>(std::forward<_Tuple>(__t))...); }
 
   template <typename _Tp, typename _Tuple>
     constexpr _Tp

libstdc++-v3/testsuite/20_util/tuple/make_from_tuple/1.cc

@@ -20,6 +20,12 @@
 #include <tuple>
 #include <testsuite_hooks.h>
 
+#ifndef __cpp_lib_make_from_tuple
+# error "Feature-test macro for make_from_tuple missing."
+#elif __cpp_lib_make_from_tuple < 201606
+# error "Feature-test macro for make_from_tuple has the wrong value."
+#endif
+
 template <class T, class U, class V>
 struct ThreeParam
 {