Fix wasm-c-api trap message format issue (#644)

And fix two compile warnings.

core/shared/platform/windows/win_thread.c

@@ -141,7 +141,7 @@ os_thread_cleanup(void *retval)
     BH_FREE(thread_data);
 }
 
-static unsigned
+static unsigned __stdcall
 os_thread_wrapper(void *arg)
 {
     os_thread_data *thread_data = arg;