I'm playing around with the `DEP_NAME_KEY=value` feature in the context of multiple `-sys` crates. Here's a [demo workspace](https://github.com/christianheussy/sys_crate_metadata). I'm getting an undefined reference error and I think I'm not entirely understanding how this works. I thought that `bar`'s dependency on `foo` and `foo`'s link against `libfoo` would be sufficient here. Do I need to point `cc` in `bar`'s build script at `foo`'s `OUT_DIR` to make this work? Any help understanding how this works would be awesome.

```
  = note: /usr/bin/ld: /home/ANT.AMAZON.COM/heussy/sandbox/rust/sys_crate_metadata/target/debug/deps/libbar-9432b7a2a9fce76e.rlib(bar.o): in function `call_bar':
          /home/ANT.AMAZON.COM/heussy/sandbox/rust/sys_crate_metadata/bar/bar.c:5: undefined reference to `call_foo'
          collect2: error: ld returned 1 exit status
```