[gcc r13-5214] libstdc++: Fix --with-default-libstdcxx-abi=gcc4-compatible build

[Jonathan Wakely]

https://gcc.gnu.org/g:d694a3d57535fbb3737dd583b15b69e0845a5846

commit r13-5214-gd694a3d57535fbb3737dd583b15b69e0845a5846
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Mon Jan 16 15:52:20 2023 +0000

    libstdc++: Fix --with-default-libstdcxx-abi=gcc4-compatible build
    
    When building src/c++20/tzdb.cc we currently get a build error for
    --with-default-libstdcxx-abi=gcc4-compatible because std::chrono::tzdb
    and related types are not declared for the gcc4-compatible ABI (unless
    --disable-libstdcxx-dual-abi is also used, so that the gcc4-compatible
    ABI is the only one built).
    
    Define _GLIBCXX_USE_CXX11_ABI in tzdb.cc so that for a dual-abi build we
    always build it for the cxx11 ABI.
    
    libstdc++-v3/ChangeLog:
    
            * src/c++20/tzdb.cc (_GLIBCXX_USE_CXX11_ABI): Define to 1.

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

diff --git a/libstdc++-v3/src/c++20/tzdb.cc b/libstdc++-v3/src/c++20/tzdb.cc
index 2ce53d38768..20399b91e47 100644
--- a/libstdc++-v3/src/c++20/tzdb.cc
+++ b/libstdc++-v3/src/c++20/tzdb.cc
@@ -25,6 +25,9 @@
 // The -Wabi warnings in this file are all for non-exported symbols.
 #pragma GCC diagnostic ignored "-Wabi"
 
+// In the usual dual-abi build, std::chrono::tzdb is only defined for cxx11.
+#define _GLIBCXX_USE_CXX11_ABI 1
+
 #include <chrono>
 #include <fstream>    // ifstream
 #include <sstream>    // istringstream