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.
{
    constexpr uint64_t min_disk_space = 52428800; 
    uint64_t free_bytes_available = fs::space(dir).available;
    return free_bytes_available >= min_disk_space + additional_bytes;
}
std::streampos GetFileSize(const char* path, std::streamsize max) {
    std::ifstream file{path, std::ios::binary};
    file.ignore(max);
    return file.gcount();
}
/**
 * Interpret a string argument as a boolean.
 *
 * The definition of LocaleIndependentAtoi<int>() requires that non-numeric string values
 * like "foo", return 0. This means that if a user unintentionally supplies a
 * non-integer argument here, the return value is always false. This means that
 * -foo=false does what the user probably expects, but -foo=true is well defined
 * but does not do what they probably expected.
 *
 * The return value of LocaleIndependentAtoi<int>(...) is zero when given input not
 * representable as an int.
 *
 * For a more extensive discussion of this topic (and a wide range of opinions
 * on the Right Way to change this code), see PR12713.
 */
static bool InterpretBool(const std::string& strValue)