Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/perf/util/pstack.c b/tools/perf/util/pstack.c
index 797fe1a..80ff41f 100644
--- a/tools/perf/util/pstack.c
+++ b/tools/perf/util/pstack.c
@@ -5,11 +5,12 @@
  * (c) 2010 Arnaldo Carvalho de Melo <acme@redhat.com>
  */
 
-#include "util.h"
 #include "pstack.h"
 #include "debug.h"
 #include <linux/kernel.h>
+#include <linux/zalloc.h>
 #include <stdlib.h>
+#include <string.h>
 
 struct pstack {
 	unsigned short	top;