PR libstdc++/82716 avoid stupid -Wmismatched-tags warnings

	PR libstdc++/82716
	* include/std/array (tuple_size, tuple_element): Change class-key
	from class to struct, to avoid annoying Clang warnings.

From-SVN: r254077

libstdc++-v3/ChangeLog

 2017-10-25  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/82716
+	* include/std/array (tuple_size, tuple_element): Change class-key
+	from class to struct, to avoid annoying Clang warnings.
+
 	PR libstdc++/79283
 	* src/filesystem/ops.cc (read_symlink): Handle st_size being zero.
 	* src/filesystem/std-ops.cc (read_symlink): Likewise.

libstdc++-v3/include/std/array

@@ -339,7 +339,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// tuple_size
   template<typename _Tp>
-    class tuple_size;
+    struct tuple_size;
 
   /// Partial specialization for std::array
   template<typename _Tp, std::size_t _Nm>
@@ -348,7 +348,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   /// tuple_element
   template<std::size_t _Int, typename _Tp>
-    class tuple_element;
+    struct tuple_element;
 
   /// Partial specialization for std::array
   template<std::size_t _Int, typename _Tp, std::size_t _Nm>