Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/build/feature/test-fortify-source.c b/tools/build/feature/test-fortify-source.c
index c9f398d..c8a5719 100644
--- a/tools/build/feature/test-fortify-source.c
+++ b/tools/build/feature/test-fortify-source.c
@@ -1,3 +1,4 @@
+// SPDX-License-Identifier: GPL-2.0
 #include <stdio.h>
 
 int main(void)