Add prepareUnitOfWork method to RecoveryUnit:
/**
 * Must be called after beginUnitOfWork and before calling either abortUnitOfWork or
 * commitUnitOfWork. Transitions the current transaction (unit of work) to the
 * "prepared" state. Must be overridden by storage engines that support prepared
 * transactions.
 */
virtual void RecoveryUnit::prepareUnitOfWork(Timestamp timestamp) {
	uasserted(ErrorCodes::PreparedTransactionsNotSupported,
                 "This storage engine does not support prepared transactions");
}