[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

llvm-svn: 286007

libcxx/test/std/strings/string.view/string.view.access/data.pass.cpp

@@ -39,7 +39,7 @@ int main () {
     test ( U"a", 1 );
 #endif
 
-#if _LIBCPP_STD_VER > 11
+#if TEST_STD_VER > 11
     {
     constexpr const char *s = "ABC";
     constexpr std::basic_string_view<char> sv( s, 2 );