[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

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@271108 91177308-0d34-0410-b5e6-96231b3b80d8

test/libcxx/experimental/utilities/tuple/header.tuple.synop/includes.pass.cpp

@@ -7,15 +7,14 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: c++98, c++03, c++11
 // <experimental/tuple>
 
 #include <experimental/tuple>
 
 int main()
 {
-#if _LIBCPP_STD_VER > 11
-# ifndef _LIBCPP_TUPLE
-#   error "<experimental/tuple> must include <tuple>"
-# endif
-#endif /* _LIBCPP_STD_VER > 11 */
+#ifndef _LIBCPP_TUPLE
+#  error "<experimental/tuple> must include <tuple>"
+#endif
 }