[libcxx] [test] Replace _LIBCPP_STD_VER with TEST_STD_VER.

This replaces every occurrence of _LIBCPP_STD_VER in the tests with
TEST_STD_VER. Additionally, for every affected
file, #include "test_macros.h" is being added explicitly if it wasn't
already there.

https://reviews.llvm.org/D26294

git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@286007 91177308-0d34-0410-b5e6-96231b3b80d8

test/std/strings/string.view/string.view.ops/compare.pointer.pass.cpp

@@ -14,6 +14,7 @@
 #include <string_view>
 #include <cassert>
 
+#include "test_macros.h"
 #include "constexpr_char_traits.hpp"
 
 int sign ( int x ) { return x > 0 ? 1 : ( x < 0 ? -1 : 0 ); }
@@ -112,7 +113,7 @@ int main()
     }
 #endif
 
-#if _LIBCPP_STD_VER > 11
+#if TEST_STD_VER > 11
     {
     typedef std::basic_string_view<char, constexpr_char_traits<char>> SV;
     constexpr SV  sv1;