Fix missing #includes in system/core.

Change-Id: I4736e8c4f7bb8bb03640d26d58243efaa67dc75c
diff --git a/toolbox/getevent.c b/toolbox/getevent.c
index da83ec3..c58eb5d 100644
--- a/toolbox/getevent.c
+++ b/toolbox/getevent.c
@@ -10,6 +10,7 @@
 #include <sys/poll.h>
 #include <linux/input.h>
 #include <errno.h>
+#include <unistd.h>
 
 #include "getevent.h"