Introduce an overflow irep that takes lvalues as arguments

In order to use `__builtin_add_overflow` and the likes, one has to introduce additional objects the address of which can be taken. To avoid such overhead when building goto programs directly, it would be desirable to have variants of the overflow intrinsics that take lvalues as (optional) parameters so that both is-there-an-overflow and the actual value can be assigned in a single instruction.