Fix use of non-constexpr C++14 addressof

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@284325 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/include/experimental/optional b/include/experimental/optional
index ebe11e6..57c5335 100644
--- a/include/experimental/optional
+++ b/include/experimental/optional
@@ -488,7 +488,7 @@
     {
         _LIBCPP_ASSERT(this->__engaged_, "optional operator-> called for disengaged value");
 #ifndef _LIBCPP_HAS_NO_BUILTIN_ADDRESSOF
-        return _VSTD::addressof(this->__val_);
+        return __builtin_addressof(this->__val_);
 #else
         return __operator_arrow(__has_operator_addressof<value_type>{});
 #endif