Supply missing move ctor in __bind_r, though this one will eventually be defaulted

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@131408 91177308-0d34-0410-b5e6-96231b3b80d8

include/functional

@@ -1704,6 +1704,10 @@ class __bind_r
 public:
     typedef _R result_type;
 
+    _LIBCPP_INLINE_VISIBILITY
+    __bind_r(__bind_r&& __b)
+        : base(_STD::move(__b)) {}
+
     template <class _G, class ..._BA>
       _LIBCPP_INLINE_VISIBILITY
       explicit __bind_r(_G&& __f, _BA&& ...__bound_args)