bin.rs

extern crate lib;
fn main() {
    lib::test();
}

gistfile1.txt

C:\msys64\home\Peter\test> rustc -g lib.rs
C:\msys64\home\Peter\test> rustc -g bin.rs --extern lib=lib.dll
error: cannot satisfy dependencies so `std` only shows up once
help: having upstream crates all available in one format will likely make this go away
error: cannot satisfy dependencies so `core` only shows up once
help: having upstream crates all available in one format will likely make this go away
error: cannot satisfy dependencies so `collections` only shows up once
help: having upstream crates all available in one format will likely make this go away
error: cannot satisfy dependencies so `rustc_unicode` only shows up once
help: having upstream crates all available in one format will likely make this go away
error: cannot satisfy dependencies so `alloc` only shows up once
help: having upstream crates all available in one format will likely make this go away
error: cannot satisfy dependencies so `libc` only shows up once
help: having upstream crates all available in one format will likely make this go away
error: cannot satisfy dependencies so `rand` only shows up once
help: having upstream crates all available in one format will likely make this go away
error: aborting due to 7 previous errors

lib.rs

#![crate_type = "dylib"]
pub fn test() {
    println!("Hello world!")
}