Workaround deprecation warning on Clang with C++20

[offa]

Compilation on Clang with C++20 (or later) and bundled fmt 8.x causes a deprecation warning:

In file included from […]/spdlog/example/example.cpp:132:
In file included from […]/spdlog/include/spdlog/sinks/daily_file_sink.h:10:
In file included from […]/spdlog/include/spdlog/fmt/chrono.h:18:
[…]/spdlog/include/spdlog/fmt/bundled/chrono.h:324:24: fatal error: 'codecvt<char32_t, char, __mbstate_t>' is deprecated [-Wdeprecated-declarations]
  using codecvt = std::codecvt<CodeUnit, char, std::mbstate_t>;
                       ^
[…]/spdlog/include/spdlog/fmt/bundled/chrono.h:358:5: note: in instantiation of function template specialization 'fmt::detail::write_codecvt<char32_t>' requested here
    write_codecvt(unit, in, loc);
    ^

This has been fixed in fmt 9.x according to it's upstream PR (fmtlib/fmt#2725)

Related

• Fix codecvt warning (#2408) fmtlib/fmt#2725
• fmt/chrono.h: use of deprecated std::codecvt class template which is deprecated as of C++20 fmtlib/fmt#2408
• Update fmt lib to v9.0.0 #2471

[gabime]

Thanks @offa