Move from memcpy to memcpy_s.

Change-Id: If7d53c6e54428f01f14528c3f281331d308af56a
diff --git a/inc/hf/std.h b/inc/hf/std.h
index 73c7d1c..f502346 100644
--- a/inc/hf/std.h
+++ b/inc/hf/std.h
@@ -30,3 +30,4 @@
  * have a constraint handler that panics.
  */
 void memset_s(void *dest, rsize_t destsz, int ch, rsize_t count);
+void memcpy_s(void *dest, rsize_t destsz, const void *src, rsize_t count);