Add generic folding function and use in CCP

Add generic folding function and use in CCP

The current folding routines have a very cumbersome interface, make them
harder to use, and not a obvious how to extend.

This change is to create a new interface for the folding routines, and
show how it can be used by calling it from CCP.

This does not make a significant change to the behaviour of CCP.  In
general it should produce the same code as before; however it is
possible that an instruction that takes 32-bit integers as inputs and
the result is not a 32-bit integer or bool will not be folded as before.