[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
diff --git a/libcxx/test/support/is_transparent.h b/libcxx/test/support/is_transparent.h
index d76b005..5416893 100644
--- a/libcxx/test/support/is_transparent.h
+++ b/libcxx/test/support/is_transparent.h
@@ -10,8 +10,10 @@
 #ifndef TRANSPARENT_H
 #define TRANSPARENT_H
 
+#include "test_macros.h"
+
 // testing transparent
-#if _LIBCPP_STD_VER > 11
+#if TEST_STD_VER > 11
 
 struct transparent_less
 {