Auto merge of #8832 - Alexendoo:duplicate-mod, r=Manishearth

Add `duplicate_mod` lint

Inspired by #8827, warns if there's a single file that is loaded by more than one `mod` item

```rust,ignore
// lib.rs
mod a;
mod b;
```
```rust,ignore
// a.rs
#[path = "./b.rs"]
mod b;
```

It adds a `canonicalize` call per `mod file;` encountered, which I don't think should be too heavy

Integration tests with common modules, e.g. [`test_utils`](https://github.com/rust-lang/rust-clippy/tree/2038084cf2253b57cf8b405ab000a92b68346f43/tests/test_utils) doesn't trigger it as each test is compiled separately, however I couldn't figure out a good way to add a test for that

changelog: Add [`duplicate_mod`] lint

0 files changed, 0 insertions, 0 deletions