fn main() {
    // Crypto features warning
    #[cfg(not(any(feature = "backend-gnupg-bin", feature = "backend-gpgme")))]
    {
        compile_error!("no crypto backend selected, must set any of these features: backend-gnupg-bin, backend-gpgme");
    }

    // GPG cryptography
    #[cfg(any(feature = "backend-gpgme", feature = "backend-gnupg-bin"))]
    println!("cargo:rustc-cfg=feature=\"_crypto-gpg\"");
}