Add link flags.

build.rs

@@ -5,14 +5,16 @@
 #![feature(io)]
 
 use std::old_io::process::{Command, ProcessExit, StdioContainer};
-
+use std::os;
 
 fn main() {
+    let out_dir = os::getenv("OUT_DIR").unwrap();
     let result = Command::new("make")
         .args(&["-f", "makefile.cargo"])
         .stdout(StdioContainer::InheritFd(1))
         .stderr(StdioContainer::InheritFd(2))
         .status()
         .unwrap();
     assert_eq!(result, ProcessExit::ExitStatus(0));
+    println!("cargo:rustc-flags=-L native={}", out_dir);
 }