Implement LWG 2770 - Make tuple_size<T> defined for all T
git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@286779 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/tuple b/include/tuple
index 9f6661f..251443e 100644
--- a/include/tuple
+++ b/include/tuple
@@ -84,7 +84,7 @@
constexpr T make_from_tuple(Tuple&& t); // C++17
// 20.4.1.4, tuple helper classes:
-template <class T> class tuple_size; // undefined
+template <class T> class tuple_size;
template <class... T> class tuple_size<tuple<T...>>;
template <class T>
constexpr size_t tuple_size_v = tuple_size<T>::value; // C++17