Implement N3672, optional<T>.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@189772 91177308-0d34-0410-b5e6-96231b3b80d8

src/optional.cpp

@@ -0,0 +1,25 @@
+//===------------------------ optional.cpp --------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "optional"
+
+namespace std  // purposefully not using versioning namespace
+{
+
+#ifdef _LIBCPP_HAS_NO_DEFAULTED_FUNCTIONS
+
+bad_optional_access::~bad_optional_access() {}
+
+#else
+
+bad_optional_access::~bad_optional_access() = default;
+
+#endif
+
+}  // std