sched: Be explicit with loading of the waketime variable

Explicilty load the timer waketime variable into local variables in
sched_timer_kick().  Change the optimization level from Os to O2.
This helps gcc to avoid unnecessary reloads from memory in the common
stepper_event() case.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/simulator/main.c

@@ -76,7 +76,7 @@ timer_read_time(void)
 }
 
 uint8_t
-timer_try_set_next(uint32_t next)
+timer_try_set_next(unsigned int next)
 {
     return 1;
 }