Add timeval_compare helper function

Change-Id: Id75727a150912ff778a4fa32ad56467da33a6324
Signed-off-by: Christopher Head <chead@zaber.com>
Reviewed-on: http://openocd.zylin.com/4379
Tested-by: jenkins
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>

src/helper/time_support.h

@@ -38,6 +38,7 @@
 
 int timeval_subtract(struct timeval *result, struct timeval *x, struct timeval *y);
 int timeval_add_time(struct timeval *result, long sec, long usec);
+int timeval_compare(const struct timeval *x, const struct timeval *y);
 
 /** @returns gettimeofday() timeval as 64-bit in ms */
 int64_t timeval_ms(void);