kbuild: Don't try to add '-fcatch-undefined-behavior' flag

This is no longer a valid option in clang, it was removed in 3.5, which
we don't support.

https://github.com/llvm/llvm-project/commit/cb3f812b6b9fab8f3b41414f24e90222170417b4



Signed-off-by: Nathan Chancellor <natechancellor@gmail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>