docs(rustc): make hello() public
Running the example code [here](https://doc.rust-lang.org/rustc/what-is-rustc.html#basic-usage) throws error:
```
error[E0603]: function `hello` is private
--> src/main.rs:4:10
|
4 | foo::hello();
| ^^^^^
```
Making `hello()` public fixes the problem.
bors
37551e9396