rtc: convert LEAP_YEAR into an inline

- the LEAP_YEAR macro is buggy - it references its arg multiple times.
  Fix this by turning it into a C function.

- give it a more approriate name

- Move it to rtc.h so that other .c files can use it, instead of copying it.

Cc: dann frazier <dannf@hp.com>
Acked-by: Alessandro Zummo <alessandro.zummo@towertech.it>
Cc: stephane eranian <eranian@googlemail.com>
Cc: "Luck, Tony" <tony.luck@intel.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/include/linux/rtc.h b/include/linux/rtc.h
index 4046b75..60f88a7 100644
--- a/include/linux/rtc.h
+++ b/include/linux/rtc.h
@@ -99,6 +99,7 @@
 
 #ifdef __KERNEL__
 
+#include <linux/types.h>
 #include <linux/interrupt.h>
 
 extern int rtc_month_days(unsigned int month, unsigned int year);
@@ -232,6 +233,11 @@
 int rtc_unregister(rtc_task_t *task);
 int rtc_control(rtc_task_t *t, unsigned int cmd, unsigned long arg);
 
+static inline bool is_leap_year(unsigned int year)
+{
+	return (!(year % 4) && (year % 100)) || !(year % 400);
+}
+
 #endif /* __KERNEL__ */
 
 #endif /* _LINUX_RTC_H_ */