ubsan: Silence W=1 warnings in self-test

Silence a handful of W=1 warnings in the UBSan selftest, which set
variables without using them. For example:

   lib/test_ubsan.c:101:6: warning: variable 'val1' set but not used [-Wunused-but-set-variable]
     101 |         int val1 = 10;
         |             ^

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202401310423.XpCIk6KO-lkp@intel.com/
Reviewed-by: Marco Elver <elver@google.com>
Signed-off-by: Kees Cook <keescook@chromium.org>

lib/Makefile

@@ -69,6 +69,7 @@ obj-$(CONFIG_HASH_KUNIT_TEST) += test_hash.o
 obj-$(CONFIG_TEST_IDA) += test_ida.o
 obj-$(CONFIG_TEST_UBSAN) += test_ubsan.o
 CFLAGS_test_ubsan.o += $(call cc-disable-warning, vla)
+CFLAGS_test_ubsan.o += $(call cc-disable-warning, unused-but-set-variable)
 UBSAN_SANITIZE_test_ubsan.o := y
 obj-$(CONFIG_TEST_KSTRTOX) += test-kstrtox.o
 obj-$(CONFIG_TEST_LIST_SORT) += test_list_sort.o

lib/test_ubsan.c

@@ -23,8 +23,8 @@ static void test_ubsan_divrem_overflow(void)
 static void test_ubsan_shift_out_of_bounds(void)
 {
 	volatile int neg = -1, wrap = 4;
-	int val1 = 10;
-	int val2 = INT_MAX;
+	volatile int val1 = 10;
+	volatile int val2 = INT_MAX;
 
 	UBSAN_TEST(CONFIG_UBSAN_SHIFT, "negative exponent");
 	val1 <<= neg;