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.
{
    LOCK(cs_dir_locks);
    dir_locks.erase(fs::PathToString(directory / lockfile_name));
}
void ReleaseDirectoryLocks()
{
    LOCK(cs_dir_locks);
    dir_locks.clear();
}
bool DirIsWritable(const fs::path& directory)
{
    fs::path tmpFile = GetUniquePath(directory);
    FILE* file = fsbridge::fopen(tmpFile, "a");
    if (!file) return false;
    fclose(file);
    remove(tmpFile);
    return true;
}
bool CheckDiskSpace(const fs::path& dir, uint64_t additional_bytes)