[tz] Error in Scandinavian tz data

[Paul Eggert]

On 2023-06-28 01:17, Stephen Colebourne via tz wrote:
> I believe that if tzdb provided a fixed offset pre-1970, but one
> linked to LMT or common practice in that location

For timestamps before 1970 we could approximate LMT along with a time 
zone abbreviation saying that the UT offset is approximate. Something 
equivalent to this, say:

   Zone America/New_York	-5:00	-	c-05	1970 Jan 1 0u
			-5:00	US	E%sT

   Zone Asia/Tokyo	9:00	-	c+09	1970 Jan 1 0u
			9:00	Japan	J%sT

The idea would be that a time zone abbreviation "c+NN" stands for "circa 
+NN", where the exact offset is unspecified. Software that cares whether 
an offset is approximate could look in the abbreviation for leading "c+" 
and "c-" (along with looking for "-00", which would continue to have its 
current meaning). POSIX allows "c+" and "c-" at the start of time zone 
abbreviations so this would pass POSIX muster.

This sort of thing could be generated automatically from the current data.