Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/virtio/xen/xen.h b/tools/virtio/xen/xen.h
new file mode 100644
index 0000000..f569387
--- /dev/null
+++ b/tools/virtio/xen/xen.h
@@ -0,0 +1,6 @@
+#ifndef XEN_XEN_STUB_H
+#define XEN_XEN_STUB_H
+
+#define xen_domain() 0
+
+#endif