Add time_since_genesis()

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/fio_time.h b/fio_time.h
index 5fd3847..27520b0 100644
--- a/fio_time.h
+++ b/fio_time.h
@@ -7,6 +7,7 @@
 extern uint64_t mtime_since(const struct timeval *, const struct timeval *);
 extern uint64_t mtime_since_now(const struct timeval *);
 extern uint64_t time_since_now(const struct timeval *);
+extern uint64_t time_since_genesis(void);
 extern uint64_t mtime_since_genesis(void);
 extern uint64_t utime_since_genesis(void);
 extern void usec_spin(unsigned int);