CVC4 causes segmentation faults when used from original repo.

[kfriedberger]

We currently use a modified version of CVC4 from https://github.com/kfriedberger/CVC4 where all finalizers are disabled to avoid several SegFaults. The problem appears sometimes on Java8 and more often on Java11. The original issue can be found at cvc5/cvc5#2846.
With all finalizers disabled, we do not have memory cleanup of CVC4 objects and leak memory as soon as the Java wrapper for such an CVC4 object is removed.

Possible steps to improve this:

• find the cause why finalizers are not working.
• replace finalizers by some management of WeakReferences like in other parts of our software.
• optimal solution: integrate our solution into the original CVC4 repository and avoid using and maintaining our own repository.

[kfriedberger]

CVC4 is superseeded by CVC5. JavaSMT will support both solvers for some time and then drop support for CVC4.