`#[no_mangle]` should not be applied to non-ASCII items

Items with an ASCII name and `#[no_mangle]` should not compile.

input:
```rust
#[no_mangle]
pub fn ぽ() {}

pub fn main() {}
```

output: compiled.

expected: rustc's output 
```bash
error[[E0754]](https://doc.rust-lang.org/stable/error_codes/E0754.html): `#[no_mangle]` requires ASCII identifier
 --> src/main.rs:2:1
  |
2 | pub fn ぽ() {}
  | ^^^^^^^^^^^
```
