mntent.h requires stdio.h

Change-Id:	If69f64cf088dedb19602bf47627d03400abb9095
diff --git a/libc/include/mntent.h b/libc/include/mntent.h
index 468ff74..b83da1f 100644
--- a/libc/include/mntent.h
+++ b/libc/include/mntent.h
@@ -28,6 +28,7 @@
 #ifndef _MNTENT_H_
 #define _MNTENT_H_
 
+#include <stdio.h>
 
 #define MNTTYPE_IGNORE "ignore"