Restructure and tidy configure.ac
Restructure and tidy configure.ac

No behavioral changes.

peterdettman/secp256k1,bitcoin/secp256k1,ElementsProject/secp256k1-zkp,bitcoin/secp256k1,evoskuil/secp256k1,afk11/secp256k1,evoskuil/secp256k1,bitcoin/secp256k1,ElementsProject/secp256k1-zkp,peterdettman/secp256k1,bitcoin-core/secp256k1,afk11/secp256k1,bitcoin/secp256k1,afk11/secp256k1,bitcoin-core/secp256k1,evoskuil/secp256k1,evoskuil/secp256k1,afk11/secp256k1,evoskuil/secp256k1,bitcoin/secp256k1,afk11/secp256k1