timezone handling regression in glibc 2.21

A regression in the zic utility in vivid's glibc 2.21 is causing weirdness in the tzdata package when used on i386:

vivid amd64:
$ TZ="PST+8PDT" date --date="2006-07-15 13:30 +0500"
Sat Jul 15 01:30:00 PDT 2006

vivid i386:
$ TZ="PST+8PDT" date --date="2006-07-15 13:30 +0500"
Sat Jul 15 00:30:00 PST 2006

utopic i386:
$ TZ="PST+8PDT" date --date="2006-07-15 13:30 +0500"
Sat Jul 15 01:30:00 PDT 2006

This is causing the test-parse-date.t test in the mercurial package to fail, causing a FTBFS.

ProblemType: Bug
DistroRelease: Ubuntu 15.04
Package: libc6 2.21-0ubuntu4
ProcVersionSignature: Ubuntu 3.19.0-20.20-generic 3.19.8
Uname: Linux 3.19.0-20-generic x86_64
ApportVersion: 2.17.2-0ubuntu1.1
Architecture: amd64
CurrentDesktop: Unity
Date: Thu Jun 4 14:24:00 2015
Dependencies:
 gcc-5-base 5.1~rc1-0ubuntu1
 libc6 2.21-0ubuntu4
 libgcc1 1:5.1~rc1-0ubuntu1
 multiarch-support 2.21-0ubuntu4
InstallationDate: Installed on 2013-11-26 (554 days ago)
InstallationMedia: Ubuntu 13.10 "Saucy Salamander" - Release amd64 (20131016.1)
SourcePackage: glibc
UpgradeStatus: Upgraded to vivid on 2015-03-07 (89 days ago)