Working on "Use std::filesystem. Remove Boost Filesystem & System" #20744, I found an unfortunate [pitfall](https://github.com/bitcoin/bitcoin/pull/20744#issuecomment-946046666) -- `boost/process.hpp` depends on `boost::filesystem` when cross-compiling for Windows. It happens in Guix environment as well.

The goal of this issue is to discuss and find a solution to get rid of `boost::filesystem`.
error = strprintf("Invalid parameter %s", argv[i]);
            return false;
        }
        std::optional<util::SettingsValue> value = InterpretValue(keyinfo, val, *flags, error);
        if (!value) return false;
        m_settings.command_line_options[keyinfo.name].push_back(*value);
    }
    
    if (auto* includes = util::FindKey(m_settings.command_line_options, "includeconf")) {
        const util::SettingsSpan values{*includes};
        
        if (!values.empty()) {
            error = "-includeconf cannot be used from commandline; -includeconf=" + values.begin()->write();
            return false; 
        }
    }
    return true;
}
std::optional<unsigned int> ArgsManager::GetArgFlags(const std::string& name) const
{
    LOCK(cs_args);
    for (const auto& arg_map : m_available_args) {
        const auto search = arg_map.second.find(name);
        if (search != arg_map.second.end()) {
            return search->second.m_flags;
        }
    }
    return std::nullopt;
}
const fs::path& ArgsManager::GetBlocksDirPath() const