Add all the relational operators to std::experimental::optional. Also update bad_optional_access to match the Library Fundamentals draft standard. This is not all of the upcoming changes to optional, though.

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@223775 91177308-0d34-0410-b5e6-96231b3b80d8

test/utilities/optional/optional.nullops/equal.pass.cpp

@@ -0,0 +1,41 @@
+//===----------------------------------------------------------------------===//
+//
+//                     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.
+//
+//===----------------------------------------------------------------------===//
+
+
+// <optional>
+
+// template <class T> constexpr bool operator==(const optional<T>& x, nullopt_t) noexcept;
+// template <class T> constexpr bool operator==(nullopt_t, const optional<T>& x) noexcept;
+
+#include <experimental/optional>
+
+int main()
+{
+#if _LIBCPP_STD_VER > 11
+    using std::experimental::optional;
+    using std::experimental::nullopt_t;
+    using std::experimental::nullopt;
+    
+    {
+    typedef int T;
+    typedef optional<T> O;
+    
+    constexpr O o1;     // disengaged
+    constexpr O o2{1};  // engaged
+
+    static_assert (  (nullopt == o1), "" );
+    static_assert ( !(nullopt == o2), "" );
+    static_assert (  (o1 == nullopt), "" );
+    static_assert ( !(o2 == nullopt), "" );
+
+    static_assert (noexcept(nullopt == o1), "");
+    static_assert (noexcept(o1 == nullopt), "");
+    }
+#endif
+}