Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/perf/include/bpf/unistd.h b/tools/perf/include/bpf/unistd.h
new file mode 100644
index 0000000..ca7877f
--- /dev/null
+++ b/tools/perf/include/bpf/unistd.h
@@ -0,0 +1,10 @@
+// SPDX-License-Identifier: LGPL-2.1
+
+#include <bpf.h>
+
+static int (*bpf_get_current_pid_tgid)(void) = (void *)BPF_FUNC_get_current_pid_tgid;
+
+static pid_t getpid(void)
+{
+	return bpf_get_current_pid_tgid();
+}