[libcxx] Improve tests to use the UNSUPPORTED lit directive

Quite a few libcxx tests seem to follow the format:
 #if _LIBCPP_STD_VER > X
   // Do test.
 #else
   // Empty test.
 #endif
We should instead use the UNSUPPORTED lit directive to exclude the test on
earlier C++ standards. This gives us a more accurate number of test passes
for those standards and avoids unnecessary conflicts with other lit
directives on the same tests.

Reviewers: bcraig, ericwf, mclow.lists

Differential revision: http://reviews.llvm.org/D20730

llvm-svn: 271108

libcxx/test/std/experimental/optional/optional.object/optional.object.ctor/default.pass.cpp

@@ -7,6 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: c++98, c++03, c++11
 // <optional>
 
 // constexpr optional() noexcept;
@@ -15,8 +16,6 @@
 #include <type_traits>
 #include <cassert>
 
-#if _LIBCPP_STD_VER > 11
-
 using std::experimental::optional;
 
 template <class Opt>
@@ -55,13 +54,9 @@ struct X
     X();
 };
 
-#endif  // _LIBCPP_STD_VER > 11
-
 int main()
 {
-#if _LIBCPP_STD_VER > 11
     test_constexpr<optional<int>>();
     test_constexpr<optional<int*>>();
     test<optional<X>>();
-#endif  // _LIBCPP_STD_VER > 11
 }