Add cbmc --incremental regression tests as FUTURE

[tautschnig]

We have these tests in the repository, but did not include them in
either Makefile or CMake configurations. They can't work right now as
the "--incremental" command-line option doesn't yet exist, thus marking
them as "FUTURE."

This is the final PR in my push to have all regression tests in the repository included in actual regression runs.

• Each commit message has a non-empty body, explaining why the change was made.
• n/a Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• n/a The feature or user visible behaviour I have added or modified has been documented in the User Guide in doc/cprover-manual/
• Regression or unit tests are included, or existing tests cover the modified code (in this case I have detailed which ones those are in the commit message).
• n/a My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• n/a White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[martin-cs]

Yes...

I thought --incremental wasn't as much a future option as a branch thing. @peterschrammel was maintaining it at one point? I'm not sure how the tests wound up getting merged but not the code itself.

[codecov]

Codecov Report

Merging #5951 (5f1b66a) into develop (4c58926) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #5951   +/-   ##
========================================
  Coverage    74.23%   74.23%           
========================================
  Files         1431     1431           
  Lines       155291   155291           
========================================
  Hits        115287   115287           
  Misses       40004    40004           

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