HAL_ChibiOS: fixed bootloader build

libraries/AP_HAL_ChibiOS/hwdef/common/stm32_util.c

@@ -438,10 +438,14 @@ void system_halt_hook(void)
 // hook for stack overflow
 void stack_overflow(thread_t *tp)
 {
+#if !defined(HAL_BOOTLOADER_BUILD) && !defined(IOMCU_FW)
     extern void AP_stack_overflow(const char *thread_name);
     AP_stack_overflow(tp->name);
     // if we get here then we are armed and got a stack overflow. We
     // will report an internal error and keep trying to fly. We are
     // quite likely to crash anyway due to memory corruption. The
     // watchdog data should record the thread name and fault type
+#else
+    (void)tp;
+#endif
 }