Add missing <sys/cdefs.h> include

quota.h uses the __P definition, so it must include <sys/cdefs.h>.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Index: b/quota.h
===================================================================
--- a/quota.h
+++ b/quota.h
@@ -2,6 +2,7 @@
 #define GUARD_QUOTA_H
 
 #include <sys/types.h>
+#include <sys/cdefs.h>
 
 typedef u_int32_t qid_t;	/* Type in which we store ids in memory */
 typedef int64_t qsize_t;	/* Type in which we store size limitations */