Update Linux to v5.4.2

Change-Id: Idf6911045d9d382da2cfe01b1edff026404ac8fd
diff --git a/tools/build/feature/test-reallocarray.c b/tools/build/feature/test-reallocarray.c
index 8170de3..8f6743e 100644
--- a/tools/build/feature/test-reallocarray.c
+++ b/tools/build/feature/test-reallocarray.c
@@ -6,3 +6,5 @@
 {
 	return !!reallocarray(NULL, 1, 1);
 }
+
+#undef _GNU_SOURCE