Add priority_queue::value_compare (LWG 2684)

	* include/bits/stl_queue.h (priority_queue::value_compare): Define.

From-SVN: r236646

libstdc++-v3/ChangeLog

+2016-05-24  Jonathan Wakely  <jwakely@redhat.com>
+
+	* include/bits/stl_queue.h (priority_queue::value_compare): Define.
+
 2016-05-23  François Dumont  <fdumont@gcc.gnu.org>
 
 	* include/debug/safe_iterator.h

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

@@ -417,6 +417,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
       typedef typename _Sequence::const_reference           const_reference;
       typedef typename _Sequence::size_type                 size_type;
       typedef          _Sequence                            container_type;
+      // _GLIBCXX_RESOLVE_LIB_DEFECTS
+      // DR 2684. priority_queue lacking comparator typedef
+      typedef	       _Compare				    value_compare;
 
     protected:
       //  See queue::c for notes on these names.