Avoid empty include paths (i.e. cc -I "" ) as they are not supported by GCC. Fix #311

        // rustc doesn't seem to work with pkg-config's output in mingw64

        if !target.contains("windows") {

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

                // avoid empty include paths as they are not supported by GCC

                if info.include_paths.len() > 0 {

                    let paths = env::join_paths(info.include_paths).unwrap();

                    println!("cargo:include={}", paths.to_str().unwrap());

                }

                return;

            }

        }