[libc++][TZDB] Improves time zone format specifiers. (#85797)
Per [tab:time.format.spec]
%z The offset from UTC as specified in ISO 8601-1:2019, subclause
5.3.4.1. For example -0430 refers to 4 hours 30 minutes behind UTC.
If the offset is zero, +0000 is used. The modified commands %Ez and
%Oz insert a : between the hours and minutes: -04:30. If the offset
information is not available, an exception of type format_error is
thrown.
Typically the modified versions Oz or Ez would have wording like
The modified command %OS produces the locale's alternative
representation.
In this case the modified version does not depend on the locale.
This change is a preparation for formatting sys_info which has time zone
information. The function time_put<_CharT>::put() does not have proper
time zone support, therefore it's a manual implementation.
Fixes https://github.com/llvm/llvm-project/issues/78184
GitOrigin-RevId: a6fcbcce8f79adfb2e4338859f3a41fc2538bad1
3 files changed
