Add sync and an incomplete version of mdev.
diff --git a/toys.h b/toys.h
index 3c6cec9..372944e 100644
--- a/toys.h
+++ b/toys.h
@@ -14,8 +14,10 @@
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
+#include <grp.h>
#include <inttypes.h>
#include <limits.h>
+#include <pwd.h>
#include <setjmp.h>
#include <stdarg.h>
#include <stdint.h>
@@ -24,6 +26,7 @@
#include <string.h>
#include <strings.h>
#include <sys/ioctl.h>
+#include <sys/mman.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/statvfs.h>