Fix missing #includes in system/core.

Change-Id: I4736e8c4f7bb8bb03640d26d58243efaa67dc75c
diff --git a/toolbox/ioctl.c b/toolbox/ioctl.c
index 73539d1..d1cc14a 100644
--- a/toolbox/ioctl.c
+++ b/toolbox/ioctl.c
@@ -9,6 +9,7 @@
 #include <errno.h>
 #include <pthread.h>
 #include <sys/ioctl.h>
+#include <unistd.h>
 
 int ioctl_main(int argc, char *argv[])
 {