AP_HAL_SITL: dump stack trace as part of panic()

libraries/AP_HAL_SITL/system.cpp

@@ -35,6 +35,8 @@ void panic(const char *errormsg, ...)
     va_end(ap);
     printf("\n");
 
+    dump_stack_trace();
+
     if (getenv("SITL_PANIC_EXIT")) {
         // this is used on the autotest server to prevent us waiting
         // 10 hours for a timeout