Add thread sleep function

src/thread_null.c

@@ -41,6 +41,11 @@ int bh_thread_init(bh_thread_t *thread,
     return BH_NO_IMPL;
 }
 
+int bh_thread_sleep(unsigned long timeout)
+{
+    return BH_NO_IMPL;
+}
+
 /**
  * Joins the \a thread.
  *