sim/hostuart: set stdout to O_NONBLOCK to prevent blocking

When NuttX sim is connected via pipe (e.g. by an automation tool),
if the host side does not read stdout in time, the pipe buffer fills
up and write(1, ...) blocks the entire sim process. This happens
inside host_uninterruptible (irq disabled), so the NuttX scheduler
is completely frozen and all threads stop.

Set fd=1 (stdout) to O_NONBLOCK so that write() returns EAGAIN
instead of blocking. The TX data stays in the NuttX xmit buffer
and sim_tty_work retries every 1ms until the pipe has space.

Signed-off-by: ligd <liguangdi1@xiaomi.com>

Author: GUIDINGLI

arch/sim/src/sim/posix/sim_hostuart.c

@@ -111,6 +111,16 @@ void host_uart_start(void)
       host_uninterruptible_no_return(fcntl, 0, F_SETFL, flags | O_NONBLOCK);
     }
 
+  /* Set stdout to non-blocking to prevent write(1, ...) from blocking
+   * the entire sim process when the host pipe buffer is full.
+   */
+
+  flags = host_uninterruptible(fcntl, 1, F_GETFL, 0);
+  if (flags > 0)
+    {
+      host_uninterruptible_no_return(fcntl, 1, F_SETFL, flags | O_NONBLOCK);
+    }
+
   /* Restore the original terminal mode before exit */
 
   atexit(restoremode);