fix sim build

Change-Id: I6c9ffe71d0dc71b2548367b021ff7ba6f833964e
diff --git a/opcontrol/opcontrol.cpp b/opcontrol/opcontrol.cpp
index b5b82b6..9f59247 100644
--- a/opcontrol/opcontrol.cpp
+++ b/opcontrol/opcontrol.cpp
@@ -23,6 +23,7 @@
 #include <getopt.h>
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <errno.h>
 #include <fcntl.h>
 #include <signal.h>