[gcc r16-9577] libstdc++: Ensure ./tzdata.zi is present in testcase

[Jonathan Wakely]

https://gcc.gnu.org/g:623e14a2298c4c2f0a4d33b4db5d9e0e10b6aca9

commit r16-9577-g623e14a2298c4c2f0a4d33b4db5d9e0e10b6aca9
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Aug 21 14:26:39 2026 +0100

    libstdc++: Ensure ./tzdata.zi is present in testcase
    
    When libstdc++ is configured without an embedded copy of the tzdata.zi
    file (e.g. when using --with-libstdcxx-zoneinfo) this testcase can fail.
    It aborts after chrono::reload_tzdb() throws an exception due to being
    unable to load tzdata.zi from the __gnu_cxx::zoneinfo_dir_override()
    path used in the test.
    
    The test passes using the default configuration because the embedded
    tzdata.zi is used, and it passes if another test has already run and
    created ./tzdata.zi in the test's current working directory.
    
    The solution is to create a dummy ./tzdata.zi file, which only needs to
    contain a version line because we only care that chrono::reload_tzdb()
    finishes, not that it loads valid data.
    
    No other tests are affected, because they either write out a tzdata.zi
    file, or call chrono::get_tzdb() (which has a fallback to a UTC-only
    database). Only calling chrono::reload_tzdb() without a file present is
    a problem, as in this test.
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/std/time/clock/utc/leap_second_info-2.cc: Create
            empty ./tzdata.zi file.
    
    (cherry picked from commit 77c73311944d2234ecafa052f9e2b4a625b59eb6)

Diff:
---
 libstdc++-v3/testsuite/std/time/clock/utc/leap_second_info-2.cc | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/libstdc++-v3/testsuite/std/time/clock/utc/leap_second_info-2.cc b/libstdc++-v3/testsuite/std/time/clock/utc/leap_second_info-2.cc
index 090a28291c85..1cfd5edf93c2 100644
--- a/libstdc++-v3/testsuite/std/time/clock/utc/leap_second_info-2.cc
+++ b/libstdc++-v3/testsuite/std/time/clock/utc/leap_second_info-2.cc
@@ -103,6 +103,9 @@ Leap	2120	Dec	30	23:59:59	-	S
 
 int main()
 {
+  // chrono::reload_tzdb() requires ./tzdata.zi to be present.
+  std::ofstream("tzdata.zi") << "# version empty\n";
+
   test_known_leaps();
   test_future_leaps();
 }