[tz] core dumps on AIX7.1 and HPUX11.31 and tzcode 2017B.

[Kees Dekker]

>> Why are the (redefines) for tzname, daylight, altzone put under TZ_TIME_T?
>> Setting TZ_TIME_T has much more effects, and I only like to have 'own' definitions of some variables, but still use the system's time_t type).

>Name mangling is intended mostly for internal use. If we wanted to be systematic 
>about it, we would need to make the library completely independent of the 
>standard C library, and that would require renaming struct tm as well. This 
>hasn't been thought through and quite possibly there would be some issues in 
>doing that.

>That being said, if you'd like to compile with -Dtime_tz=time_t in the meantime, 
>nobody will stop you.

Thanks Paul, I understand. Anyhow, I would prefer, if possible, and if there is a similar by others,
to consider a change for the future in this region, and make the tz code completely independent
from the system libraries, except for well known types.