speedtest: some architectures require stdlib.h

Needed for atoi() and strtol().

Change-Id: Ied12a590ae983ab464c974d402cd69b2df44370d
diff --git a/speedtest/options.cc b/speedtest/options.cc
index cb360d5..96957f9 100644
--- a/speedtest/options.cc
+++ b/speedtest/options.cc
@@ -2,6 +2,7 @@
 
 #include <assert.h>
 #include <getopt.h>
+#include <stdlib.h>
 #include <string.h>
 #include <strings.h>
 #include "url.h"