stddef.h is required by offsetof()

src/kernel/Communicator.cc

@@ -24,6 +24,7 @@
 #include <time.h>
 #include <fcntl.h>
 #include <unistd.h>
+#include <stddef.h>
 #include <stdlib.h>
 #include <string.h>
 #include <pthread.h>

src/kernel/mpoller.c

@@ -16,6 +16,7 @@
   Author: Xie Han (xiehan@sogou-inc.com)
 */
 
+#include <stddef.h>
 #include <stdlib.h>
 #include "poller.h"
 #include "mpoller.h"