um: Enable FORTIFY_SOURCE

Enable FORTIFY_SOURCE so running Kunit tests can test fortified
functions.
Signed-off-by: Kees Cook <keescook@chromium.org>
Tested-by: David Gow <davidgow@google.com>
Link: https://lore.kernel.org/r/20220210003224.773957-1-keescook@chromium.org

arch/um/Kconfig

@@ -6,6 +6,7 @@ config UML
 	bool
 	default y
 	select ARCH_EPHEMERAL_INODES
+	select ARCH_HAS_FORTIFY_SOURCE
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_KCOV
 	select ARCH_HAS_STRNCPY_FROM_USER

arch/um/os-Linux/user_syms.c

 // SPDX-License-Identifier: GPL-2.0
+#define __NO_FORTIFY
 #include <linux/types.h>
 #include <linux/module.h>