[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.assign/move.pass.cpp

@@ -7,6 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: c++98, c++03, c++11
 // XFAIL: libcpp-no-exceptions
 // <optional>
 
@@ -18,8 +19,6 @@
 #include <type_traits>
 #include <cassert>
 
-#if _LIBCPP_STD_VER > 11
-
 using std::experimental::optional;
 
 struct X
@@ -42,11 +41,8 @@ struct Y {};
 
 bool X::throw_now = false;
 
-#endif  // _LIBCPP_STD_VER > 11
-
 int main()
 {
-#if _LIBCPP_STD_VER > 11
     {
         static_assert(std::is_nothrow_move_assignable<optional<int>>::value, "");
         optional<int> opt;
@@ -100,5 +96,4 @@ int main()
     {
         static_assert(std::is_nothrow_move_assignable<optional<Y>>::value, "");
     }
-#endif  // _LIBCPP_STD_VER > 11
 }