libstdc++: Update tzdata to 2025c

Import the new 2025c tzdata.zi file and new leapseconds expiry date.

libstdc++-v3/ChangeLog:

	* include/std/chrono (chrono::__detail::__get_leap_second_info):
	Update expiry date for leap seconds list.
	* src/c++20/tzdb.cc (tzdb_list::_Node::_S_read_leap_seconds):
	Likewise.
	* src/c++20/tzdata.zi: Import new file from 2025c release.

Reviewed-by: Tomasz Kamiński <[email protected]>

Author: jwakely

libstdc++-v3/include/std/chrono

@@ -3240,7 +3240,7 @@ namespace __detail
       };
       // The list above is known to be valid until (at least) this date
       // and only contains positive leap seconds.
-      const sys_seconds __expires(1766880000s); // 2025-12-28 00:00:00 UTC
+      constexpr sys_seconds __expires(1782604800s); // 2026-06-28 00:00:00 UTC
 
 #if _GLIBCXX_USE_CXX11_ABI || ! _GLIBCXX_USE_DUAL_ABI
       if (__ss > __expires)

libstdc++-v3/src/c++20/tzdata.zi

@@ -1,4 +1,4 @@
-# version 2025b
+# version 2025c
 # This zic input file is in the public domain.
 R d 1916 o - Jun 14 23s 1 S
 R d 1916 1919 - O Su>=1 23s 0 -
@@ -2951,9 +2951,7 @@ Z America/Tijuana -7:48:4 - LMT 1922 Ja 1 7u
 -8 1 PDT 1951 S 30 2
 -8 - PST 1952 Ap 27 2
 -8 1 PDT 1952 S 28 2
--8 - PST 1954
--8 CA P%sT 1961
--8 - PST 1976
+-8 CA P%sT 1967
 -8 u P%sT 1996
 -8 m P%sT 2001
 -8 u P%sT 2002 F 20

libstdc++-v3/src/c++20/tzdb.cc

@@ -1245,8 +1245,8 @@ namespace std::chrono
   pair<vector<leap_second>, bool>
   tzdb_list::_Node::_S_read_leap_seconds()
   {
-    // This list is valid until at least 2025-12-28 00:00:00 UTC.
-    auto expires = sys_days{2025y/12/28};
+    // This list is valid until at least 2026-06-28 00:00:00 UTC.
+    constexpr auto expires = sys_days{2026y/06/28};
     vector<leap_second> leaps
     {
       (leap_second)  78796800, // 1 Jul 1972