Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/arch/x86/boot/boot.h b/arch/x86/boot/boot.h
index ef5a9cc..ca866f1 100644
--- a/arch/x86/boot/boot.h
+++ b/arch/x86/boot/boot.h
@@ -1,12 +1,10 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
 /* -*- linux-c -*- ------------------------------------------------------- *
  *
  *   Copyright (C) 1991, 1992 Linus Torvalds
  *   Copyright 2007 rPath, Inc. - All Rights Reserved
  *   Copyright 2009 Intel Corporation; author H. Peter Anvin
  *
- *   This file is part of the Linux kernel, and is made available under
- *   the terms of the GNU General Public License version 2.
- *
  * ----------------------------------------------------------------------- */
 
 /*
@@ -30,8 +28,6 @@
 #include "cpuflags.h"
 
 /* Useful macros */
-#define BUILD_BUG_ON(condition) ((void)sizeof(char[1 - 2*!!(condition)]))
-
 #define ARRAY_SIZE(x) (sizeof(x) / sizeof(*(x)))
 
 extern struct setup_header hdr;
@@ -309,7 +305,7 @@
 void __attribute__((noreturn)) die(void);
 
 /* memory.c */
-int detect_memory(void);
+void detect_memory(void);
 
 /* pm.c */
 void __attribute__((noreturn)) go_to_protected_mode(void);