[PATCH] login: Assume that _HAVE_UT_* constants are defined

[Florian Weimer]

* Adhemerval Zanella:

>> +	  || __utmp_equal (&last_entry, data)))
>
> Shouldn't we check for > 0 instead of a implicit check?

The style guidelines do not have a strong preference in case of true
flags.

We could change __utmp_equal to return bool, maybe in a subsequent
cleanup.

Thanks,
Florian