Disable output buffering in tests_exhaustive.c
Disable output buffering in tests_exhaustive.c

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