printf requires \n

`printf` won't output anything unless there's a newline.

```
U:\>coreutils --version
coreutils 2026.6.16 (multi-call binary)

U:\>coreutils printf test

U:\>coreutils printf test\n
test

U:\>coreutils printf test\nmore
test

U:\>
```

Edit: `echo -n` also has the same problem.