[tz] OpenJDK/CLDR/ICU/Joda issues with Ireland change

[Paul Eggert]

J William Piggott wrote:
> Rather than requiring applications to "call localtime and gmtime ... and
> subtract the results by hand", why couldn't the function(s) used by
> tzset for the tm_gmtoff value be made available for applications?

You don't need functions. All you need is tm_gmtoff; it's simple and easy to 
explain, and is a widely-used extension to POSIX.

> Perhaps it should be documented in the glibc manual and elsewhere?

The glibc manual already documents tm_gmtoff, as do manuals for other operating 
systems that have it. Unfortunately tm_gmtoff is not standardized by C or POSIX, 
perhaps because standardizers mistakenly thought that strftime %z was enough.