Drain kqueue events to prevent WFI busy-loop

The poll()-based event loop was not consuming kqueue events on macOS,
causing the kqueue fd to remain readable after the first timer tick.
This defeated the WFI sleep optimization by making poll(..., -1) return
immediately instead of blocking when all harts are idle.

Root cause:
- Linux path: timerfd is consumed via read() after poll()
- macOS path: kqueue events were never drained after poll()
- Result: kqueue fd stays readable → poll() never blocks → 100% CPU

Author: jserv

main.c

@@ -1170,9 +1170,6 @@ static int semu_run(emu_state_t *emu)
                 pfd_count++;
             }
 #endif
-#ifdef __APPLE__
-            (void) timer_index;
-#endif
 
             /* Add UART input fd (stdin for keyboard input) */
             if (emu->uart.in_fd >= 0 && pfd_count < poll_capacity) {
@@ -1207,16 +1204,24 @@ static int semu_run(emu_state_t *emu)
             if (pfd_count > 0) {
                 int nevents = poll(pfds, pfd_count, poll_timeout);
                 if (nevents > 0) {
-#ifndef __APPLE__
-                    /* Consume timer expiration event on Linux (timerfd) */
+                    /* Consume timer expiration events to prevent fd staying
+                     * readable
+                     */
                     if (timer_index >= 0 &&
                         (pfds[timer_index].revents & POLLIN)) {
+#ifdef __APPLE__
+                        /* drain kqueue events with non-blocking kevent */
+                        struct kevent events[32];
+                        struct timespec timeout_zero = {0, 0};
+                        kevent(kq, NULL, 0, events, 32, &timeout_zero);
+#else
+                        /* Linux: read timerfd to consume expiration count */
                         uint64_t expirations;
                         ssize_t ret_read = read(wfi_timer_fd, &expirations,
                                                 sizeof(expirations));
                         (void) ret_read;
-                    }
 #endif
+                    }
                 } else if (nevents < 0 && errno != EINTR) {
                     perror("poll");
                 }