Support TZ transition times < 00:00:00.

This is needed for version-3 tz-format files; it supports time
stamps past 2037 for America/Godthab (the only entry in the tz
database for which this change is relevant).
* manual/time.texi (TZ Variable): Document transition times
from -167:59:59 through -00:00:01.
* time/tzset.c (tz_rule): Time of day is now signed.
(__tzset_parse_tz): Parse negative time of day.

1 files changed, 11 insertions, 1 deletions

diff --git a/manual/time.texi b/manual/time.texi
index c65a73e29f..e7e8647ee2 100644
--- a/manual/time.texi
+++ b/manual/time.texi
@@ -2087,7 +2087,7 @@ between @code{1} and @code{12}.
 The @var{time} fields specify when, in the local time currently in
 effect, the change to the other time occurs.  If omitted, the default is
 @code{02:00:00}.  The hours part of the time fields can range from
-0 through 167; this is an extension to POSIX.1, which allows
+@minus{}167 through 167; this is an extension to POSIX.1, which allows
 only the range 0 through 24.
 
 Here are some example @code{TZ} values, including the appropriate
@@ -2123,6 +2123,16 @@ is a placeholder.
 WART4WARST,J1/0,J365/25
 @end smallexample
 
+Western Greenland Time (WGT) and Western Greenland Summer Time (WGST)
+are 3 hours behind UTC in the winter.  Its clocks follow the European
+Union rules of springing forward by one hour on March's last Sunday at
+01:00 UTC (@minus{}02:00 local time) and falling back on October's
+last Sunday at 01:00 UTC (@minus{}01:00 local time).
+
+@smallexample
+WGT3WGST,M3.5.0/-2,M10.5.0/-1
+@end smallexample
+
 The schedule of Daylight Saving Time in any particular jurisdiction has
 changed over the years.  To be strictly correct, the conversion of dates
 and times in the past should be based on the schedule that was in effect