[tz] A small first step in merging NetBSD changes into tzcode

[Paul Eggert]

On 2023-01-05 00:01, Robert Elz wrote:

> I'd still recommend the proposed solution though, implement err() for
> systems that don't have it, rather than cluttering the code. 

Much of the code already used the C-standard fprintf+strerror approach, 
and for programs like zdump I'd rather not bother testing and 
configuring an optional reimplementation of BSD's 'err' function (or the 
GNU 'error' function for that matter) on platforms that lack it; it's 
not worth the hassle.

The main point of the change was to improve the quality of the 
diagnostics in question so that they're as good as NetBSD's modifications.