cargo check produces dead_code warnings for bin targets

[crumblingstatue]

For a project generated with cargo new --bin:

warning: function is never used: `main`, #[warn(dead_code)] on by default
 --> src/main.rs:1:1
  |
1 |   fn main() {
  |  _^ starting here...
2 | |     println!("Hello, world!");
3 | | }
  | |_^ ...ending here

[alexcrichton]

I believe this is a dupe of rust-lang/rust#38273, but thanks for the report!