v1::process does not compile under c++26

[antonvw]

Here is compile error (osx platform),

In file included from /opt/homebrew/include/boost/process/v1/system.hpp:21:
In file included from /opt/homebrew/include/boost/process/v1/detail/on_exit.hpp:12:
In file included from /opt/homebrew/include/boost/process/v1/detail/posix/on_exit.hpp:10:
In file included from /opt/homebrew/include/boost/process/v1/async.hpp:34:
In file included from /opt/homebrew/include/boost/process/v1/detail/traits.hpp:15:
In file included from /opt/homebrew/include/boost/process/v1/detail/traits/wchar_t.hpp:15:
/opt/homebrew/include/boost/process/v1/locale.hpp:79:45: error: no template named 'codecvt_utf8' in namespace ‘std’
79 | return std::locale(global_loc, new std::codecvt_utf8<wchar_t>);

see:
https://en.cppreference.com/cpp/locale/codecvt_utf8