auto merge of #864 : tomaka/cargo/fix-814, r=alexcrichton

Close #814

Unfortunately I don't really know how I'd add a test for this.
In order to try compile a library then a binary, you need to successfully compile the library, which means that you'd need to pass a valid value instead of just `-l foo`

diff --cc src/cargo/ops/cargo_rustc/mod.rs
Simple merge