Add __uncvref type for use in later patches

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@258491 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/type_traits b/include/type_traits
index 3b80a9e..f13e29f 100644
--- a/include/type_traits
+++ b/include/type_traits
@@ -1084,6 +1084,13 @@
 
 #endif  // _LIBCPP_HAS_NO_RVALUE_REFERENCES
 
+// __uncvref
+
+template <class _Tp>
+struct __uncvref  {
+    typedef typename remove_cv<typename remove_reference<_Tp>::type>::type type;
+};
+
 struct __any
 {
     __any(...);