[libc++][TZDB] Fixes %z escaping. (#125399)

The previous tested TZDB did not contain %z for the rule letters. The
usage of %z in TZDB 2024b revealed a bug in the implementation. The
patch fixes it and has been locally tested with TZDB 2024b.

Fixes #108957

(cherry picked from commit a27f3b2)

Author: mordante

libcxx/src/experimental/time_zone.cpp

@@ -668,7 +668,7 @@ __first_rule(seconds __stdoff, const vector<__tz::__rule>& __rules) {
                __continuation_end,
                __continuation.__stdoff + __save,
                chrono::duration_cast<minutes>(__save),
-               __continuation.__format},
+               chrono::__format(__continuation, __continuation.__format, __save)},
       true};
 }
 

libcxx/test/libcxx/time/time.zone/time.zone.timezone/time.zone.members/get_info.sys_time.pass.cpp

@@ -157,7 +157,6 @@ static void test_abbrev(std::string_view input, std::string_view expected) {
   TEST_LIBCPP_REQUIRE(result == expected, TEST_WRITE_CONCATENATED("\nExpected ", expected, "\nActual ", result, '\n'));
 }
 
-// This format is valid, however is not used in the tzdata.zi.
 static void percentage_z_format() {
   test_abbrev(
       R"(
@@ -188,6 +187,12 @@ Z Format 0:45 F %z)",
 R F 1999 max - Jan 5 0 -1 foo
 Z Format 0:45 F %z)",
       "-0015");
+
+  test_abbrev(
+      R"(
+Z Format -1:2:20 - LMT 1912 Ja 1 1u
+-1 - %z)",
+      "-01");
 }
 
 int main(int, const char**) {