[zxcrypt] enable some integer sanitization

Enable the integer-divide-by-zero (relevant for ARM only) and
signed-integer-overflow checkers. This will add in-code detection for
some classes of undefined integer behavior.

Limit this to zxcrypt for now, as this is just an experiment.

SEC-53: Build a system that is robust against vulnerabilities

Change-Id: I89a5aca790c7325aa5de4d153a1f53036a14c814