bug: fix warning suppressions with kunit built as module

bug: fix warning suppressions with kunit built as module

CONFIG_KUNIT is a tristate symbol but the warning suppression code in
lib/bug.c is only built if it's built-in due to it using a plain #ifdef,
rendering warning suppressions broken for kunit build as loadable module.

kunit_is_suppressed_warning() already has a stub for when kunit is
disabled so drop that guard entirely.

Link: https://lore.kernel.org/r/20260708095459.12111-1-bartosz.golaszewski@oss.qualcomm.com
Suggested-by: Albert Esteve <aesteve@redhat.com>
Cc: stable@vger.kernel.org
Fixes: 85347718ab0d ("bug/kunit: Core support for suppressing warning backtraces")
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@oss.qualcomm.com>
Reviewed-by: Albert Esteve <aesteve@redhat.com>
Reviewed-by: David Gow <david@davidgow.net>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>