ubsan: integer-overflow: depend on BROKEN to keep this out of CI

Depending on !COMPILE_TEST isn't sufficient to keep this feature out of
CI because we can't stop it from being included in randconfig builds.
This feature is still highly experimental, and is developed in lock-step
with Clang's Overflow Behavior Types[1]. Depend on BROKEN to keep it
from being enabled by anyone not expecting it.

Link: https://discourse.llvm.org/t/rfc-v2-clang-introduce-overflowbehaviortypes-for-wrapping-and-non-wrapping-arithmetic/86507

 [1]
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202505281024.f42beaa7-lkp@intel.com


Fixes: 557f8c58 ("ubsan: Reintroduce signed overflow sanitizer")
Acked-by: Eric Biggers <ebiggers@kernel.org>
Link: https://lore.kernel.org/r/20250528182616.work.296-kees@kernel.org


Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Acked-by: Marco Elver <elver@google.com>
Signed-off-by: Kees Cook <kees@kernel.org>