<stdlib.h> is required for NULL to be defined in safe_rw.c

Author: jedisct1

src/dnscrypt-proxy/safe_rw.c

@@ -7,6 +7,7 @@
 #ifndef _WIN32
 # include <poll.h>
 #endif
+#include <stdlib.h>
 #include <unistd.h>
 
 #include "safe_rw.h"