tools/timezones: update timezone database, and improve TZ compiler

Our TZ compiler is somewhat out of data, and needs to use "rearguard" format
rather than "vanguard" format.  Luckily, the Olson database has a script,
"ziguard.awk", that converts between forms (this fixes Ireland DST).

On the other hand, ziguard.awk had a different form of normalizing %z than
we were used to, and we did not support some of those formats when we went
to parse.  So now we support those formats.

Tested by diffing the textual output of tools/timezones.py old vs. new.

License: GPL-3.0-or-later
Signed-off-by: Joshua Wise <[email protected]>

Author: jwise

LICENSES/LicenseRef-PD-2.txt

@@ -0,0 +1,2 @@
+# This file is in the public domain, so clarified as of
+# 2009-05-17 by Arthur David Olson.

REUSE.toml

@@ -44,3 +44,8 @@ SPDX-FileCopyrightText = "Thomas Nagy, 2005-2018 (ita)"
 path = [".github/**", ".git*", "bin/boot/*", "requirements*.txt"]
 SPDX-License-Identifier = "Apache-2.0"
 SPDX-FileCopyrightText = "2025 Core Devices"
+
+[[annotations]]
+path = "resources/normal/base/tzdata/timezones_olson.txt"
+SPDX-License-Identifier = "LicenseRef-PD-2"
+SPDX-FileCopyrightText = "Arthur David Olson"