I work at a robotics integrator and we've had similar situations in our engineering team. In the end, it usually came down to talking to the client about it. These kinds of things are usually designed to protect the client from someone coming back later and demanding money. The code you'll be writing for this project will be owned by them and therefore never require a license agreement. Are the function and code-snippets truly unique and novel or are they common implementation patterns that you apply to many projects? Just remember that if you write a for-loop for someone else doesn't mean you can't ever use a for-loop ever again. So talk to the client. Let them know you have these functions and code snippets that you've used prior and plan to use in the future. That will help clear up the root issue they're trying to protect against.
...never send to know for whom the code faults; if faults for thee.