lib/time/day_to_str.h: DAY_TO_STR(): Add macro

This macro ensures that the buffer is an array, and calculates the size.

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

lib/time/day_to_str.h

@@ -12,9 +12,14 @@
 
 #include <time.h>
 
+#include "defines.h"
+#include "sizeof.h"
 #include "string/strtcpy.h"
 
 
+#define DAY_TO_STR(str, day)   date_to_str(NITEMS(str), str, day * DAY)
+
+
 inline void date_to_str(size_t size, char buf[size], long date);