Stop hardcoding things in openssl-sys build.rs

#![feature(env, path)]

#![feature(env, path, core)]

extern crate "pkg-config" as pkg_config;

extern crate gcc;

use std::env;

fn main() {

    let target = env::var("TARGET").unwrap();

    if target.contains("android") {

        let path = env::var("OPENSSL_PATH").ok()

            .expect("Android does not provide openssl libraries, please build them yourself \

                     (instructions in the README) and provide their location through \

                     $OPENSSL_PATH.");

        println!("cargo:rustc-flags=-L native={} -l crypto:static -l ssl:static", path);

    if let Ok(info) = pkg_config::find_library("openssl") {

        build_old_openssl_shim(info.include_paths);

        return;

    }

    if target.contains("win32") || target.contains("win64") || target.contains("windows") {

        println!("cargo:rustc-flags=-l crypto -l ssl -l gdi32 -l wsock32");

        build_old_openssl_shim(vec![]);

        return;

    }

    let (libcrypto, libssl) = if env::var("TARGET").unwrap().contains("windows") {

    	("eay32", "ssl32")

    } else {

    	("crypto", "ssl")

    };

    let err = match pkg_config::find_library("openssl") {

        Ok(info) => {

            build_old_openssl_shim(info.include_paths);

            return;

        }

        Err(err) => err,

    let mode = if env::var_os("OPENSSL_STATIC").is_some() {

    	"static"

    } else {

    	"dylib"

    };

    // pkg-config doesn't know of OpenSSL on FreeBSD 10.1 and OpenBSD uses LibreSSL

    if target.contains("bsd") {

        println!("cargo:rustc-flags=-l crypto -l ssl");

        build_old_openssl_shim(vec![]);

        return;

    if let Ok(lib_dir) = env::var("OPENSSL_LIB_DIR") {

    	println!("cargo:rustc-flags=-L native={}", lib_dir);

    }

    println!("cargo:rustc-flags=-l {0}={1} -l {0}={2}", mode, libcrypto, libssl);

    let mut include_dirs = vec![];

    if let Ok(include_dir) = env::var("OPENSSL_INCLUDE_DIR") {

    	include_dirs.push(Path::new(include_dir));

    }

    panic!("unable to find openssl: {}", err);

    build_old_openssl_shim(include_dirs);

}

fn build_old_openssl_shim(include_paths: Vec<Path>) {