Add NITEMS(arr) to get the number of elements of an array

Signed-off-by: Alejandro Colomar <alx@kernel.org>

lib/defines.h

@@ -171,6 +171,8 @@ static inline void memzero(void *ptr, size_t size)
 #define SCALE DAY
 #endif
 
+#define NITEMS(arr)  (sizeof((arr)) / sizeof((arr)[0]))
+
 /* Copy string pointed by B to array A with size checking.  It was originally
    in lmain.c but is _very_ useful elsewhere.  Some setuid root programs with
    very sloppy coding used to assume that BUFSIZ will always be enough...  */