[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/string.view/string.view.comparison/opeq.string_view.string.pass.cpp

@@ -7,6 +7,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+// UNSUPPORTED: c++98, c++03, c++11
 // <string>
 
 // template<class charT, class traits, class Allocator>
@@ -17,8 +18,6 @@
 #include <experimental/string_view>
 #include <cassert>
 
-#if _LIBCPP_STD_VER > 11
-
 template <class S>
 void
 test(const std::string &lhs, S rhs, bool x)
@@ -49,6 +48,4 @@ int main()
     test("abcdefghijklmnopqrst", S("abcdefghijklmnopqrst"), true);
     }
 }
-#else
-int main () {}
-#endif
+