Fix missing const on set::count. Patch from Andrey Khalyavin

llvm-svn: 289204
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 41b4d6c8ffedfe3a31749d29c40298ca340f1ba9
diff --git a/include/set b/include/set
index ac69e08..606af72 100644
--- a/include/set
+++ b/include/set
@@ -672,7 +672,7 @@
     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);}
+    count(const _K2& __k) const                    {return __tree_.__count_unique(__k);}
 #endif
     _LIBCPP_INLINE_VISIBILITY
     iterator lower_bound(const key_type& __k)