lib: fortify_kunit: build without structleak plugin

Building allmodconfig with aarch64-linux-gnu-gcc (Debian 11.3.0-6),
fortify_kunit with strucleak plugin enabled makes the stack frame size
to grow too large:

lib/fortify_kunit.c:140:1: error: the frame size of 2368 bytes is larger than 2048 bytes [-Werror=frame-larger-than=]

Turn off the structleak plugin checks for fortify_kunit.
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Anders Roxell <anders.roxell@linaro.org>
Signed-off-by: Kees Cook <keescook@chromium.org>

lib/Makefile

@@ -379,6 +379,7 @@ obj-$(CONFIG_OVERFLOW_KUNIT_TEST) += overflow_kunit.o
 CFLAGS_stackinit_kunit.o += $(call cc-disable-warning, switch-unreachable)
 obj-$(CONFIG_STACKINIT_KUNIT_TEST) += stackinit_kunit.o
 CFLAGS_fortify_kunit.o += $(call cc-disable-warning, unsequenced)
+CFLAGS_fortify_kunit.o += $(DISABLE_STRUCTLEAK_PLUGIN)
 obj-$(CONFIG_FORTIFY_KUNIT_TEST) += fortify_kunit.o
 obj-$(CONFIG_STRSCPY_KUNIT_TEST) += strscpy_kunit.o
 obj-$(CONFIG_SIPHASH_KUNIT_TEST) += siphash_kunit.o