Introduce intermediate build target for std.

This gives a place for common functions to be defined.

Change-Id: Ifac38e647ab1042a00d224a58e28a0e6807fa60c
diff --git a/test/hftest/hftest_common.c b/test/hftest/hftest_common.c
index 5a3b348..e1b4602 100644
--- a/test/hftest/hftest_common.c
+++ b/test/hftest/hftest_common.c
@@ -16,10 +16,10 @@
 
 #include "hftest_common.h"
 
-#include "hf/arch/std.h"
 #include "hf/arch/vm/power_mgmt.h"
 
 #include "hf/memiter.h"
+#include "hf/std.h"
 
 #include "hftest.h"