[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/std/experimental/string.view/string.view.capacity/capacity.pass.cpp b/libcxx/test/std/experimental/string.view/string.view.capacity/capacity.pass.cpp
index 9f5d86f..a5108bf 100644
--- a/libcxx/test/std/experimental/string.view/string.view.capacity/capacity.pass.cpp
+++ b/libcxx/test/std/experimental/string.view/string.view.capacity/capacity.pass.cpp
@@ -23,7 +23,7 @@
 
 template<typename SV>
 void test1 () {
-#if _LIBCPP_STD_VER > 11
+#if TEST_STD_VER > 11
     {
     constexpr SV sv1;
     static_assert ( sv1.size() == 0, "" );