Fix warning

src/core/disk_ops/unistd/disk_unistd_global.c

@@ -536,7 +536,7 @@ int starpu_unistd_global_full_write(void *base STARPU_ATTRIBUTE_UNUSED, void *ob
 	return starpu_unistd_global_write(base, obj, ptr, 0, size);
 }
 
-#if HAVE_AIO_H
+#if defined(HAVE_AIO_H)
 void * starpu_unistd_global_async_full_read (void * base, void * obj, void ** ptr, size_t * size, unsigned dst_node)
 {
         struct starpu_unistd_global_obj *tmp = (struct starpu_unistd_global_obj *) obj;