Libstdc++: Fix bootstrap failure for cross without tm.tm_zone [PR119550]

In r15-8491-g778c28c70f8573 I added a use of the Autoconf macro
AC_STRUCT_TIMEZONE, but that requires a link-test for the global tzname
object if tm.tm_zone isn't supported. That link-test isn't allowed for
cross-compilation, so bootstrap fails if tm.tm_zone isn't supported.

Since libstdc++ only cares about tm.tm_zone and won't use tzname anyway,
we don't need the link-test. Replace AC_STRUCT_TIMEZONE with a custom
macro that only checks for tm.tm_zone. We can improve on the Autoconf
macro by checking it's a suitable type, which isn't actually checked by
AC_STRUCT_TIMEZONE.

libstdc++-v3/ChangeLog:

	PR libstdc++/119550
	* acinclude.m4 (GLIBCXX_STRUCT_TM_TM_ZONE): New macro.
	* config.h.in: Regenerate.
	* configure: Regenerate.
	* configure.ac: Use GLIBCXX_STRUCT_TM_TM_ZONE.
	* include/bits/chrono_io.h (__formatter_chrono::_M_c): Check
	_GLIBCXX_USE_STRUCT_TM_TM_ZONE instead of
	_GLIBCXX_HAVE_STRUCT_TM_TM_ZONE.

5 files changed, 109 insertions, 192 deletions

diff --git a/libstdc++-v3/acinclude.m4 b/libstdc++-v3/acinclude.m4
index e668d2d..02fd349e 100644
--- a/libstdc++-v3/acinclude.m4
+++ b/libstdc++-v3/acinclude.m4
@@ -5745,6 +5745,41 @@ AC_DEFUN([GLIBCXX_ZONEINFO_DIR], [
 ])
 
 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
+])
+
+dnl
 dnl Check whether lock tables can be aligned to avoid false sharing.
 dnl
 dnl Defines:
diff --git a/libstdc++-v3/config.h.in b/libstdc++-v3/config.h.in
index be151f4..77bbaf1 100644
--- a/libstdc++-v3/config.h.in
+++ b/libstdc++-v3/config.h.in
@@ -74,10 +74,6 @@
    don't. */
 #undef HAVE_DECL_STRNLEN
 
-/* Define to 1 if you have the declaration of `tzname', and to 0 if you don't.
-   */
-#undef HAVE_DECL_TZNAME
-
 /* Define to 1 if you have the <dirent.h> header file. */
 #undef HAVE_DIRENT_H
 
@@ -412,9 +408,6 @@
 /* Define to 1 if `d_type' is a member of `struct dirent'. */
 #undef HAVE_STRUCT_DIRENT_D_TYPE
 
-/* Define to 1 if `tm_zone' is a member of `struct tm'. */
-#undef HAVE_STRUCT_TM_TM_ZONE
-
 /* Define if strxfrm_l is available in <string.h>. */
 #undef HAVE_STRXFRM_L
 
@@ -506,17 +499,9 @@
 /* Define to 1 if the target supports thread-local storage. */
 #undef HAVE_TLS
 
-/* Define to 1 if your `struct tm' has `tm_zone'. Deprecated, use
-   `HAVE_STRUCT_TM_TM_ZONE' instead. */
-#undef HAVE_TM_ZONE
-
 /* Define if truncate is available in <unistd.h>. */
 #undef HAVE_TRUNCATE
 
-/* Define to 1 if you don't have `tm_zone' but do have the external array
-   `tzname'. */
-#undef HAVE_TZNAME
-
 /* Define to 1 if you have the <uchar.h> header file. */
 #undef HAVE_UCHAR_H
 
@@ -605,9 +590,6 @@
 /* Define to 1 if you have the ANSI C header files. */
 #undef STDC_HEADERS
 
-/* Define to 1 if your <sys/time.h> declares `struct tm'. */
-#undef TM_IN_SYS_TIME
-
 /* Version number of package */
 #undef VERSION
 
@@ -906,6 +888,9 @@
 /* Define to restrict std::__basic_file<> to stdio APIs. */
 #undef _GLIBCXX_USE_STDIO_PURE
 
+/* Define if struct tm has a tm_zone member. */
+#undef _GLIBCXX_USE_STRUCT_TM_TM_ZONE
+
 /* Define if struct stat has timespec members. */
 #undef _GLIBCXX_USE_ST_MTIM
 
diff --git a/libstdc++-v3/configure b/libstdc++-v3/configure
index 67d2b8c..56d0bcb 100755
--- a/libstdc++-v3/configure
+++ b/libstdc++-v3/configure
@@ -2731,63 +2731,6 @@ $as_echo "$ac_res" >&6; }
   eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno
 
 } # ac_fn_c_check_decl
-
-# ac_fn_c_check_member LINENO AGGR MEMBER VAR INCLUDES
-# ----------------------------------------------------
-# Tries to find if the field MEMBER exists in type AGGR, after including
-# INCLUDES, setting cache variable VAR accordingly.
-ac_fn_c_check_member ()
-{
-  as_lineno=${as_lineno-"$1"} as_lineno_stack=as_lineno_stack=$as_lineno_stack
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for $2.$3" >&5
-$as_echo_n "checking for $2.$3... " >&6; }
-if eval \${$4+:} false; then :
-  $as_echo_n "(cached) " >&6
-else
-  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-$5
-int
-main ()
-{
-static $2 ac_aggr;
-if (ac_aggr.$3)
-return 0;
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-  eval "$4=yes"
-else
-  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-$5
-int
-main ()
-{
-static $2 ac_aggr;
-if (sizeof ac_aggr.$3)
-return 0;
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-  eval "$4=yes"
-else
-  eval "$4=no"
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-fi
-eval ac_res=\$$4
-	       { $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_res" >&5
-$as_echo "$ac_res" >&6; }
-  eval $as_lineno_stack; ${as_lineno_stack:+:} unset as_lineno
-
-} # ac_fn_c_check_member
 cat >config.log <<_ACEOF
 This file contains any messages produced by compilers while
 running configure, to aid debugging if configure makes a mistake.
@@ -12337,7 +12280,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12340 "configure"
+#line 12283 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12443,7 +12386,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12446 "configure"
+#line 12389 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -16239,7 +16182,7 @@ $as_echo "$glibcxx_cv_atomic_long_long" >&6; }
   # Fake what AC_TRY_COMPILE does.
 
     cat > conftest.$ac_ext << EOF
-#line 16242 "configure"
+#line 16185 "configure"
 int main()
 {
   typedef bool atomic_type;
@@ -16274,7 +16217,7 @@ $as_echo "$glibcxx_cv_atomic_bool" >&6; }
     rm -f conftest*
 
     cat > conftest.$ac_ext << EOF
-#line 16277 "configure"
+#line 16220 "configure"
 int main()
 {
   typedef short atomic_type;
@@ -16309,7 +16252,7 @@ $as_echo "$glibcxx_cv_atomic_short" >&6; }
     rm -f conftest*
 
     cat > conftest.$ac_ext << EOF
-#line 16312 "configure"
+#line 16255 "configure"
 int main()
 {
   // NB: _Atomic_word not necessarily int.
@@ -16345,7 +16288,7 @@ $as_echo "$glibcxx_cv_atomic_int" >&6; }
     rm -f conftest*
 
     cat > conftest.$ac_ext << EOF
-#line 16348 "configure"
+#line 16291 "configure"
 int main()
 {
   typedef long long atomic_type;
@@ -16501,7 +16444,7 @@ $as_echo "mutex" >&6; }
   # unnecessary for this test.
 
     cat > conftest.$ac_ext << EOF
-#line 16504 "configure"
+#line 16447 "configure"
 int main()
 {
   _Decimal32 d1;
@@ -16543,7 +16486,7 @@ ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
   # unnecessary for this test.
 
   cat > conftest.$ac_ext << EOF
-#line 16546 "configure"
+#line 16489 "configure"
 template<typename T1, typename T2>
   struct same
   { typedef T2 type; };
@@ -54482,6 +54425,65 @@ _ACEOF
   fi
 
 
+# For std::chrono formatters to use tm::tm_zone
+
+
+
+  ac_ext=cpp
+ac_cpp='$CXXCPP $CPPFLAGS'
+ac_compile='$CXX -c $CXXFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CXX -o conftest$ac_exeext $CXXFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_cxx_compiler_gnu
+
+  ac_save_CXXFLAGS="$CXXFLAGS"
+  CXXFLAGS="$CXXFLAGS -std=c++20"
+
+  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for tm_zone member of struct tm" >&5
+$as_echo_n "checking for tm_zone member of struct tm... " >&6; }
+if ${glibcxx_cv_tm_zone+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+
+    cat confdefs.h - <<_ACEOF >conftest.$ac_ext
+/* end confdefs.h.  */
+#include <time.h>
+
+int
+main ()
+{
+struct tm t{}; t.tm_zone = (char*)0;
+
+  ;
+  return 0;
+}
+_ACEOF
+if ac_fn_cxx_try_compile "$LINENO"; then :
+  glibcxx_cv_tm_zone=yes
+else
+  glibcxx_cv_tm_zone=no
+
+fi
+rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
+
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $glibcxx_cv_tm_zone" >&5
+$as_echo "$glibcxx_cv_tm_zone" >&6; }
+
+  if test $glibcxx_cv_tm_zone = yes; then
+
+$as_echo "#define _GLIBCXX_USE_STRUCT_TM_TM_ZONE 1" >>confdefs.h
+
+  fi
+
+  CXXFLAGS="$ac_save_CXXFLAGS"
+  ac_ext=c
+ac_cpp='$CPP $CPPFLAGS'
+ac_compile='$CC -c $CFLAGS $CPPFLAGS conftest.$ac_ext >&5'
+ac_link='$CC -o conftest$ac_exeext $CFLAGS $CPPFLAGS $LDFLAGS conftest.$ac_ext $LIBS >&5'
+ac_compiler_gnu=$ac_cv_c_compiler_gnu
+
+
+
 # For src/c++11/shared_ptr.cc alignment.
 
 
@@ -54697,112 +54699,6 @@ ac_compiler_gnu=$ac_cv_c_compiler_gnu
 
 
 
-{ $as_echo "$as_me:${as_lineno-$LINENO}: checking whether struct tm is in sys/time.h or time.h" >&5
-$as_echo_n "checking whether struct tm is in sys/time.h or time.h... " >&6; }
-if ${ac_cv_struct_tm+:} false; then :
-  $as_echo_n "(cached) " >&6
-else
-  cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-#include <sys/types.h>
-#include <time.h>
-
-int
-main ()
-{
-struct tm tm;
-				     int *p = &tm.tm_sec;
-				     return !p;
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_compile "$LINENO"; then :
-  ac_cv_struct_tm=time.h
-else
-  ac_cv_struct_tm=sys/time.h
-fi
-rm -f core conftest.err conftest.$ac_objext conftest.$ac_ext
-fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_struct_tm" >&5
-$as_echo "$ac_cv_struct_tm" >&6; }
-if test $ac_cv_struct_tm = sys/time.h; then
-
-$as_echo "#define TM_IN_SYS_TIME 1" >>confdefs.h
-
-fi
-
-ac_fn_c_check_member "$LINENO" "struct tm" "tm_zone" "ac_cv_member_struct_tm_tm_zone" "#include <sys/types.h>
-#include <$ac_cv_struct_tm>
-
-"
-if test "x$ac_cv_member_struct_tm_tm_zone" = xyes; then :
-
-cat >>confdefs.h <<_ACEOF
-#define HAVE_STRUCT_TM_TM_ZONE 1
-_ACEOF
-
-
-fi
-
-if test "$ac_cv_member_struct_tm_tm_zone" = yes; then
-
-$as_echo "#define HAVE_TM_ZONE 1" >>confdefs.h
-
-else
-  ac_fn_c_check_decl "$LINENO" "tzname" "ac_cv_have_decl_tzname" "#include <time.h>
-"
-if test "x$ac_cv_have_decl_tzname" = xyes; then :
-  ac_have_decl=1
-else
-  ac_have_decl=0
-fi
-
-cat >>confdefs.h <<_ACEOF
-#define HAVE_DECL_TZNAME $ac_have_decl
-_ACEOF
-
-  { $as_echo "$as_me:${as_lineno-$LINENO}: checking for tzname" >&5
-$as_echo_n "checking for tzname... " >&6; }
-if ${ac_cv_var_tzname+:} false; then :
-  $as_echo_n "(cached) " >&6
-else
-  if test x$gcc_no_link = xyes; then
-  as_fn_error $? "Link tests are not allowed after GCC_NO_EXECUTABLES." "$LINENO" 5
-fi
-cat confdefs.h - <<_ACEOF >conftest.$ac_ext
-/* end confdefs.h.  */
-#include <time.h>
-#if !HAVE_DECL_TZNAME
-extern char *tzname[];
-#endif
-
-int
-main ()
-{
-return tzname[0][0];
-  ;
-  return 0;
-}
-_ACEOF
-if ac_fn_c_try_link "$LINENO"; then :
-  ac_cv_var_tzname=yes
-else
-  ac_cv_var_tzname=no
-fi
-rm -f core conftest.err conftest.$ac_objext \
-    conftest$ac_exeext conftest.$ac_ext
-fi
-{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $ac_cv_var_tzname" >&5
-$as_echo "$ac_cv_var_tzname" >&6; }
-  if test $ac_cv_var_tzname = yes; then
-
-$as_echo "#define HAVE_TZNAME 1" >>confdefs.h
-
-  fi
-fi
-
-
 # Define documentation rules conditionally.
 
 # See if makeinfo has been installed and is modern enough
diff --git a/libstdc++-v3/configure.ac b/libstdc++-v3/configure.ac
index fe0cdde..a6c01b2 100644
--- a/libstdc++-v3/configure.ac
+++ b/libstdc++-v3/configure.ac
@@ -572,6 +572,9 @@ GLIBCXX_EMERGENCY_EH_ALLOC
 # For src/c++20/tzdb.cc defaults.
 GLIBCXX_ZONEINFO_DIR
 
+# For std::chrono formatters to use tm::tm_zone
+GLIBCXX_STRUCT_TM_TM_ZONE
+
 # For src/c++11/shared_ptr.cc alignment.
 GLIBCXX_CHECK_ALIGNAS_CACHELINE
 
@@ -584,8 +587,6 @@ GLIBCXX_CHECK_FILEBUF_NATIVE_HANDLES
 # For std::text_encoding
 GLIBCXX_CHECK_TEXT_ENCODING
 
-AC_STRUCT_TIMEZONE
-
 # Define documentation rules conditionally.
 
 # See if makeinfo has been installed and is modern enough
diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index 3a5bc56..d872109 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -905,7 +905,7 @@ namespace __format
 	  // time zone info available for the time in __tm.
 	  __tm.tm_isdst = -1;
 
-#ifdef _GLIBCXX_HAVE_STRUCT_TM_TM_ZONE
+#ifdef _GLIBCXX_USE_STRUCT_TM_TM_ZONE
 	  // POSIX.1-2024 adds tm.tm_zone which will be used for %Z.
 	  // BSD has had tm_zone since 1987 but as char* so cast away const.
 	  if constexpr (__is_time_point_v<_Tp>)