include stdlib for malloc() and free()

Reviewed-by: Rich Salz <rsalz@openssl.org>

GH: #1174
diff --git a/fuzz/driver.c b/fuzz/driver.c
index de51574..c530fed 100644
--- a/fuzz/driver.c
+++ b/fuzz/driver.c
@@ -9,6 +9,7 @@
  */
 #include <stdint.h>
 #include <unistd.h>
+#include <stdlib.h>
 #include <openssl/opensslconf.h>
 #include "fuzzer.h"