Commit c3fd455 changed LibTimeZone to fall back to the system time zone
when we fail to parse the TZ environment variable. This behavior differs
from both our LibC and glibc; they abort parsing and default to UTC.
This changes LibTimeZone to behave the same way to avoid a very awkward
situation where some parts of the codebase thinks the timezone is UTC,
and others think the timezone is whatever /etc/timezone indicates.
Some time zones, like "Asia/Shanghai", use a set of DST rules that end
before present day. In these cases, we should fall back to last possible
RULE entry from the TZDB. The time zone compiler published by IANA (zic)
performs the same fallback starting with version 2 of the time zone file
format.
This is no longer needed now that LibTimeZone is included within LibC.
Remove the direct linkage so that others do not mistakenly copy-paste
the CMakeLists text elsewhere.
Instead of only having dummy functions that don't work with any input,
let's at least support one time zone: 'UTC'. This matches the basic
Temporal implementation for engines without ECMA-262, for example.
This is a rather naive implementation, but serves as a first pass at
determining the GMT offset for a time zone at a particular point in
time. This implementation ignores DST (because we are not parsing any
RULE entries yet), and ignores any offset patterns of the form "Mon>4"
or "lastSun".
