improper_ctypes lint triggers for functions returning `()`

[crumblingstatue]

6fa17b4 made the improper_ctypes lint trigger for tuples, but as far as I understand, returning () is equivalent to returning c_void, and therefore should be allowed.

Here is an example:

extern "C" {
    pub fn foo() -> ();
}

fn main() {
}

foo.rs:2:21: 2:23 warning: found Rust tuple type in foreign module; consider using a struct instead`, #[warn(improper_ctypes)] on by default
foo.rs:2     pub fn foo() -> ();
                             ^~

[eefriedman]

Yes, stupid mistake; I'll fix it. (As a workaround, you can write pub fn foo();.)

[steveklabnik]

since #27315 was merged i'm closing