Fix bug 20740 - std::set/std::map don't support heterogeneous lookup for count(). Thanks to Jim Porter for the bug report

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@216353 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/set b/include/set
index b9e776d..22d794d 100644
--- a/include/set
+++ b/include/set
@@ -663,6 +663,12 @@
     _LIBCPP_INLINE_VISIBILITY
     size_type      count(const key_type& __k) const
         {return __tree_.__count_unique(__k);}
+#if _LIBCPP_STD_VER > 11
+    template <typename _K2>
+    _LIBCPP_INLINE_VISIBILITY
+    typename enable_if<__is_transparent<_Compare, _K2>::value,size_type>::type
+    count(const _K2& __k)                  {return __tree_.__count_unique(__k);}
+#endif
     _LIBCPP_INLINE_VISIBILITY
     iterator lower_bound(const key_type& __k)
         {return __tree_.lower_bound(__k);}
@@ -1066,6 +1072,12 @@
     _LIBCPP_INLINE_VISIBILITY
     size_type      count(const key_type& __k) const
         {return __tree_.__count_multi(__k);}
+#if _LIBCPP_STD_VER > 11
+    template <typename _K2>
+    _LIBCPP_INLINE_VISIBILITY
+    typename enable_if<__is_transparent<_Compare, _K2>::value,size_type>::type
+    count(const _K2& __k)                  {return __tree_.__count_multi(__k);}
+#endif
 
     _LIBCPP_INLINE_VISIBILITY
     iterator lower_bound(const key_type& __k)