Introduce intermediate build target for std.

This gives a place for common functions to be defined.

Change-Id: Ifac38e647ab1042a00d224a58e28a0e6807fa60c
diff --git a/src/cpu.c b/src/cpu.c
index 3cc15be..b2213d1 100644
--- a/src/cpu.c
+++ b/src/cpu.c
@@ -19,10 +19,10 @@
 #include <stdalign.h>
 
 #include "hf/arch/cpu.h"
-#include "hf/arch/std.h"
 
 #include "hf/api.h"
 #include "hf/dlog.h"
+#include "hf/std.h"
 #include "hf/vm.h"
 
 #include "vmapi/hf/call.h"