[libcxx] [test] Make futures.overview/future_errc.pass.cpp and launch.pass.cpp more portable.

[STL_MSFT]

Summary

Make futures.overview/future_errc.pass.cpp and launch.pass.cpp more portable.

future_errc.pass.cpp was assuming specific values, which aren't guaranteed by the Standard, and MSVC uses different ones. Update the comment, and rewrite the tests to verify the Standard's guarantees of distinctness and nonzeroness.

launch.pass.cpp also contains non-Standard assumptions. They happen to be true for MSVC, with the exception of a static_assert about bitwise NOT. Apparently for libcxx, this operator modifies only 2 bits. For MSVC, it modifies all the bits in the representation. Mark this static_assert as libcxx-specific.

[EricWF]

r274211.

test/std/thread/futures/futures.overview/future_errc.pass.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.
 //
 //===----------------------------------------------------------------------===//
 //
 // UNSUPPORTED: libcpp-has-no-threads
 
 // <future>
 
 // enum class future_errc
 // {
-//     future_already_retrieved = 1,
-//     promise_already_satisfied,
-//     no_state
-//     broken_promise,
+//     broken_promise = implementation-defined,
+//     future_already_retrieved = implementation-defined,
+//     promise_already_satisfied = implementation-defined,
+//     no_state = implementation-defined
 // };
 
 #include <future>
 
 int main()
 {
-    static_assert(static_cast<int>(std::future_errc::future_already_retrieved) == 1, "");
-    static_assert(static_cast<int>(std::future_errc::promise_already_satisfied) == 2, "");
-    static_assert(static_cast<int>(std::future_errc::no_state) == 3, "");
-    static_assert(static_cast<int>(std::future_errc::broken_promise) == 4, "");
+    static_assert(std::future_errc::broken_promise != std::future_errc::future_already_retrieved, "");
+    static_assert(std::future_errc::broken_promise != std::future_errc::promise_already_satisfied, "");
+    static_assert(std::future_errc::broken_promise != std::future_errc::no_state, "");
+    static_assert(std::future_errc::future_already_retrieved != std::future_errc::promise_already_satisfied, "");
+    static_assert(std::future_errc::future_already_retrieved != std::future_errc::no_state, "");
+    static_assert(std::future_errc::promise_already_satisfied != std::future_errc::no_state, "");
+
+    static_assert(std::future_errc::broken_promise != static_cast<std::future_errc>(0), "");
+    static_assert(std::future_errc::future_already_retrieved != static_cast<std::future_errc>(0), "");
+    static_assert(std::future_errc::promise_already_satisfied != static_cast<std::future_errc>(0), "");
+    static_assert(std::future_errc::no_state != static_cast<std::future_errc>(0), "");
 }

test/std/thread/futures/futures.overview/launch.pass.cpp

 {
 #ifdef _LIBCPP_HAS_NO_STRONG_ENUMS
    LIBCPP_STATIC_ASSERT(static_cast<int>(std::launch::any) ==
                  (static_cast<int>(std::launch::async) | static_cast<int>(std::launch::deferred)), "");
 #else
     LIBCPP_STATIC_ASSERT(std::launch::any == (std::launch::async | std::launch::deferred), "");
     static_assert(std::launch(0) == (std::launch::async & std::launch::deferred), "");
     LIBCPP_STATIC_ASSERT(std::launch::any == (std::launch::async ^ std::launch::deferred), "");
-    static_assert(std::launch::deferred == ~std::launch::async, "");
+    LIBCPP_STATIC_ASSERT(std::launch::deferred == ~std::launch::async, "");
     std::launch x = std::launch::async;
     x &= std::launch::deferred;
     assert(x == std::launch(0));
     x = std::launch::async;
     x |= std::launch::deferred;
     LIBCPP_ASSERT(x == std::launch::any);
     x ^= std::launch::deferred;
     assert(x == std::launch::async);
 #endif
     static_assert(static_cast<int>(std::launch::async) == 1, "");
     static_assert(static_cast<int>(std::launch::deferred) == 2, "");
 }