[gcc r16-1120] libstdc++: Skip time zone format testing for COW std::string

[Jonathan Wakely]

https://gcc.gnu.org/g:fc198521cd3e135bc07f6a86a5ffa9c70fc3abca

commit r16-1120-gfc198521cd3e135bc07f6a86a5ffa9c70fc3abca
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Wed Jun 4 21:49:54 2025 +0100

    libstdc++: Skip time zone format testing for COW std::string
    
    This is needed when testing with -D_GLIBCXX_USE_CXX11_ABI=0 to fix:
    FAIL: std/time/format/empty_spec.cc  -std=gnu++20 (test for excess errors)
    
    libstdc++-v3/ChangeLog:
    
            * testsuite/std/time/format/empty_spec.cc: Only test time zones
            for cxx11 string ABI.

Diff:
---
 libstdc++-v3/testsuite/std/time/format/empty_spec.cc | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/libstdc++-v3/testsuite/std/time/format/empty_spec.cc b/libstdc++-v3/testsuite/std/time/format/empty_spec.cc
index ec57a6f0d209..a3c64f5211ef 100644
--- a/libstdc++-v3/testsuite/std/time/format/empty_spec.cc
+++ b/libstdc++-v3/testsuite/std/time/format/empty_spec.cc
@@ -647,6 +647,7 @@ test_leap_second()
 	  WIDEN("2012-06-30 23:59:60") );
 }
 
+#if _GLIBCXX_USE_CXX11_ABI
 template<typename Dur, typename Dur2>
 auto
 make_zoned(const sys_time<Dur2>& st, const time_zone* tz)
@@ -679,6 +680,7 @@ test_zoned_time()
   verify( make_zoned<kilodays>(st, tz),
 	  WIDEN("2022-01-08 02:00:00 EET") );
 }
+#endif
 
 template<typename Dur, typename Dur2>
 auto
@@ -725,7 +727,9 @@ test_time_points()
   test_time_point<CharT, gps_clock>(true);
   test_time_point<CharT, file_clock>(true);
   test_leap_second<CharT>();
+#if _GLIBCXX_USE_CXX11_ABI
   test_zoned_time<CharT>();
+#endif
   test_local_time_format<CharT>();
 
   test_no_empty_spec<CharT, sys_time<years>>();