Add C++11 __iterator_category_t template alias.

	* include/bits/stl_iterator_base_types.h (__iterator_category_t): Define
	for C++11.
	(_RequireInputIte): Likewise and use __enable_if_t.
	* include/std/numeric
	(__is_random_access_iter): Use __iterator_category_t.

From-SVN: r276637

libstdc++-v3/ChangeLog

 2019-10-06  François Dumont  <fdumont@gcc.gnu.org>
 
+	* include/bits/stl_iterator_base_types.h (__iterator_category_t): Define
+	for C++11.
+	(_RequireInputIte): Likewise and use __enable_if_t.
+	* include/std/numeric
+	(__is_random_access_iter): Use __iterator_category_t.
+
 	* include/bits/stl_algo.h (copy_n): Add __glibcxx_requires_can_increment
 	debug checks.
 	* testsuite/25_algorithms/copy_n/debug/1_neg.cc: New.

libstdc++-v3/include/bits/stl_iterator_base_types.h

@@ -208,11 +208,14 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   //@}
 
 #if __cplusplus >= 201103L
+  template<typename _Iter>
+    using __iterator_category_t
+      = typename iterator_traits<_Iter>::iterator_category;
+
   template<typename _InIter>
-    using _RequireInputIter = typename
-      enable_if<is_convertible<typename
-		iterator_traits<_InIter>::iterator_category,
-			       input_iterator_tag>::value>::type;
+    using _RequireInputIter =
+      __enable_if_t<is_convertible<__iterator_category_t<_InIter>,
+				   input_iterator_tag>::value>;
 #endif
 
 _GLIBCXX_END_NAMESPACE_VERSION

libstdc++-v3/include/std/numeric

@@ -230,8 +230,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   /// @{
 
   /// @cond undocumented
-  template<typename _It, typename _Traits = iterator_traits<_It>,
-	   typename _Cat = typename _Traits::iterator_category>
+  template<typename _It, typename _Cat = __iterator_category_t<_It>>
     using __is_random_access_iter
       = is_base_of<random_access_iterator_tag, _Cat>;
   /// @endcond