[Bug libstdc++/119550] [15 Regression] cross compilation of libstdc++ fail for arm-none-eabi due to tzname tests since g:778c28c70f85

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119550

--- Comment #9 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Something like this:

dnl
dnl Check for a tm_zone member in struct tm.
dnl
dnl This member is defined as const char* in Glibc, newlib, POSIX.1-2024,
dnl and as char* in BSD (including macOS).
dnl
dnl Defines:
dnl  _GLIBCXX_USE_STRUCT_TM_TM_ZONE if struct tm has a tm_zone member.
dnl
AC_DEFUN([GLIBCXX_STRUCT_TM_TM_ZONE], [

  AC_LANG_SAVE
  AC_LANG_CPLUSPLUS
  ac_save_CXXFLAGS="$CXXFLAGS"
  CXXFLAGS="$CXXFLAGS -std=c++20"

  AC_CACHE_CHECK([for tm_zone member of struct tm], glibcxx_cv_tm_zone, [
    AC_COMPILE_IFELSE([AC_LANG_PROGRAM([#include <time.h>
        ],
        [struct tm t{}; t.tm_zone = (char*)0;]
        )],
        [glibcxx_cv_tm_zone=yes],
        [glibcxx_cv_tm_zone=no]
      )
    ])

  if test $glibcxx_cv_tm_zone = yes; then
    AC_DEFINE(_GLIBCXX_USE_STRUCT_TM_TM_ZONE, 1,
              [Define if struct tm has a tm_zone member.])
  fi

  CXXFLAGS="$ac_save_CXXFLAGS"
  AC_LANG_RESTORE
])