title: Unable to add to the rustc-link-search path of a dependency
body: <p>I am trying to build a test app using <a href="https://github.com/tupshin/cassandra-rs" rel="nofollow">cassandra-rs</a> which uses the <a href="https://github.com/datastax/cpp-driver/" rel="nofollow">DataStax CPP driver</a>. I am using <code>cargo 0.6.0 (ec9398e 2015-09-29) (built from git)</code>. </p>
  
  <p>My DataStax driver is not located in the standard directories Cargo looks in.</p>
  
  <p>I added a build script specifying the path to the DataStax driver: </p>
  
  <pre><code>fn main() {
      println!("cargo:rustc-link-search={}", "/path/to/dir/");
  }
  </code></pre>
  
  <p>Here is my Cargo.toml:</p>
  
  <pre><code>[package]
  name = "castest"
  version = "0.1.0"
  build = "build.rs"
  
  [dependencies]
  cassandra="*"
  </code></pre>
  
  <p>But <code>cargo build --verbose</code> shows that the additional search directory is not included when building.</p>
  
  <p>The package that the build is actually failing on is cql_bindgen which is a dependency of cassandra-rs. In that project there is this build.rs:</p>
  
  <pre><code>fn main() {
      println!("cargo:rustc-flags=-l dylib=crypto");
      println!("cargo:rustc-flags=-l dylib=ssl");
      println!("cargo:rustc-flags=-l dylib=stdc++");
      println!("cargo:rustc-flags=-l dylib=uv");
      println!("cargo:rustc-link-search={}", "/usr/lib/");
      println!("cargo:rustc-link-search={}", "/usr/local/lib64");
      println!("cargo:rustc-link-lib=static=cassandra_static");
  }
  </code></pre>
  
  <p>How can I add additional libraries or otherwise override configuration in my project that is set in dependent projects?</p>