On my Linux Mint 19.1:
```bash
$ umask
0022
```

After the first run of `bitcoin-qt -sysperm=false` the `0700` permissions are expected for both the datadir (`~/.bitcoin`) and the walletdir (`~/.bitcoin/wallets`).

Actually, the directories are created with such access permissions:
```bash
$ stat ~/.bitcoin | grep Uid
Access: (0755/drwxr-xr-x)  Uid: ( 1000/ hebasto)   Gid: ( 1000/ hebasto)
$ stat ~/.bitcoin/wallets | grep Uid
Access: (0755/drwxr-xr-x)  Uid: ( 1000/ hebasto)   Gid: ( 1000/ hebasto)
```

Refs:
- #4286
- #13371
- #13389

NOTE: reading through the initial PR #4286 makes me think it was controversial. Is it a better and simpler way to just get rid of `-sysperm` option? I believe a user who needs this option can easily run `chown` command.
{
    fs::path path;
    if (!GetSettingsPath(&path,  false)) {
        return true; 
    }
    LOCK(cs_args);
    m_settings.rw_settings.clear();
    std::vector<std::string> read_errors;
    if (!util::ReadSettings(path, m_settings.rw_settings, read_errors)) {
        SaveErrors(read_errors, errors);
        return false;
    }
    for (const auto& setting : m_settings.rw_settings) {
        KeyInfo key = InterpretKey(setting.first); 
        if (!GetArgFlags('-' + key.name)) {
            LogPrintf("Ignoring unknown rw_settings value %s\n", setting.first);
        }
    }
    return true;
}
bool ArgsManager::WriteSettingsFile(std::vector<std::string>* errors, bool backup) const