56b07badf0
The definitions of the new C++20 members of std::stringstream etc are missing when --with-default-libstdcxx-abi=gcc4-compatible is used, because all the explicit instantiations in src/c++20/sstream-inst.cc are skipped. This ensures the contents of that file are compiled with the new ABI, so the same set of symbols are exported regardless of which ABI is active by default. libstdc++-v3/ChangeLog: * src/c++20/sstream-inst.cc (_GLIBCXX_USE_CXX11_ABI): Define to select new ABI.