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.
if (g_zmq_notification_interface) {
        RegisterValidationInterface(g_zmq_notification_interface);
    }
#endif
     
    fReindex = args.GetBoolArg("-reindex", false);
    bool fReindexChainState = args.GetBoolArg("-reindex-chainstate", false);
    ChainstateManager::Options chainman_opts{
        .chainparams = chainparams,
        .adjusted_time_callback = GetAdjustedTime,
    };
    Assert(!ApplyArgsManOptions(args, chainman_opts));  
     
    CacheSizes cache_sizes = CalculateCacheSizes(args, g_enabled_filter_types.size());
    LogPrintf("Cache configuration:\n");
    LogPrintf("* Using %.1f MiB for block index database\n", cache_sizes.block_tree_db * (1.0  1024  1024));
    if (args.GetBoolArg("-txindex", DEFAULT_TXINDEX)) {
        LogPrintf("* Using %.1f MiB for transaction index database\n", cache_sizes.tx_index * (1.0  1024  1024));
    }
    for (BlockFilterType filter_type : g_enabled_filter_types) {
        LogPrintf("* Using %.1f MiB for %s block filter index database\n",
                  cache_sizes.filter_index * (1.0  1024  1024), BlockFilterTypeName(filter_type));
    }
    LogPrintf("* Using %.1f MiB for chain state database\n", cache_sizes.coins_db * (1.0  1024  1024));
    assert(!node.mempool);
    assert(!node.chainman);
    CTxMemPool::Options mempool_opts{
        .estimator = node.fee_estimator.get(),
        .check_ratio = chainparams.DefaultConsistencyChecks() ? 1 : 0,
    };