build: let configure tell us if we have address sanitizer

build: let configure tell us if we have address sanitizer

We cannot really rely on __has_feature or __ADDRESS_SANITIZER__ in code
since we are mostly interested in the leak sanitizer and there is
neither a feature nor a macro for that. Early version of GCC have the
address sanitizer, but not the leak sanitizer. We don't support this
configuration, but we need to build correctly either way. So, the user
is expected to enable address sanitizers only on configuration
supporting also the leak sanitizer.