Use build.rs in place of test_linking_hack
See Alex Crichton's comments at https://github.com/torproject/tor/commit/a8ac21fbb5f22b68ffa019b575085c142293bc40#commitcomment-30729271
See Alex Crichton's comments at https://github.com/torproject/tor/commit/a8ac21fbb5f22b68ffa019b575085c142293bc40#commitcomment-30729271