async support

Index: runtime/flang/async.c
--- runtime/flang/async.c.orig
+++ runtime/flang/async.c
@@ -22,7 +22,7 @@
 #include <stdlib.h>
 #include <errno.h>
 #include <string.h>
-#include <aio.h>
+#include <aio_compat.h>
 #include <signal.h>
 #else
 #include <windows.h>
