[gcc r13-4875] libstdc++: Fix Darwin bootstrap error in src/c++20/tzdb.cc

[Jonathan Wakely]

https://gcc.gnu.org/g:b358521b608f36409281a51263ace3155d28f54d

commit r13-4875-gb358521b608f36409281a51263ace3155d28f54d
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Dec 23 13:43:52 2022 +0000

    libstdc++: Fix Darwin bootstrap error in src/c++20/tzdb.cc
    
    Mach-O requires weak symbols to have a definition, so add a default
    implementation of __gnu_cxx::zoneinfo_dir_override.
    
    libstdc++-v3/ChangeLog:
    
            * src/c++20/tzdb.cc [__APPLE__] (zoneinfo_dir_override): Add
            definition.

Diff:
---
 libstdc++-v3/src/c++20/tzdb.cc | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/libstdc++-v3/src/c++20/tzdb.cc b/libstdc++-v3/src/c++20/tzdb.cc
index a02bcd4aec7..5f5c4199f65 100644
--- a/libstdc++-v3/src/c++20/tzdb.cc
+++ b/libstdc++-v3/src/c++20/tzdb.cc
@@ -52,6 +52,10 @@
 # endif
 #endif
 
+#ifndef _GLIBCXX_ZONEINFO_DIR
+# define _GLIBCXX_ZONEINFO_DIR "/usr/share/zoneinfo"
+#endif
+
 namespace __gnu_cxx
 {
 #ifdef _AIX
@@ -59,6 +63,12 @@ namespace __gnu_cxx
   const char* (*zoneinfo_dir_override)() = nullptr;
 #else
   [[gnu::weak]] const char* zoneinfo_dir_override();
+
+#ifdef __APPLE__
+  // Need a weak definition for Mach-O.
+  [[gnu::weak]] const char* zoneinfo_dir_override()
+  { return _GLIBCXX_ZONEINFO_DIR; }
+#endif
 #endif
 }
 
@@ -934,9 +944,6 @@ namespace std::chrono
     return info;
   }
 
-#ifndef _GLIBCXX_ZONEINFO_DIR
-# define _GLIBCXX_ZONEINFO_DIR "/usr/share/zoneinfo"
-#endif
  namespace
  {
     string