Install Z3

[mernst]

These instructions add z3 to the needed packages.

Without z3 installed, these commands failed under Ubuntu:

ctest . -V -L CORE -R cbmc-CORE
ctest . -V -L CORE -R book-examples-new-smt-backend-CORE

With z3 installed, the commands succeed.

A more complete list of failures that are solved by installing z3 is:

	  1 - cbmc-CORE (Failed)                                CBMC CORE
	  5 - cbmc-paths-lifo-CORE (Failed)                     CBMC CORE
	  7 - cbmc-new-smt-backend-CORE (Failed)                CBMC CORE
	  8 - cbmc-library-CORE (Failed)                        CBMC CORE
	 47 - cbmc-incr-smt2-z3-CORE (Failed)                   CBMC CORE
	157 - contracts-CORE (Failed)                           CBMC CORE
	161 - contracts-dfcc-CORE (Failed)                      CBMC CORE
	248 - book-examples-new-smt-backend-CORE (Failed)       CBMC CORE
	261 - unit (Failed)                                     CBMC CORE

• Each commit message has a non-empty body, explaining why the change was made.
• Methods or procedures I have added are documented, following the guidelines provided in CODING_STANDARD.md.
• 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).
• My commit message includes data points confirming performance improvements (if claimed).
• My PR is restricted to a single feature or bugfix.
• White-space or formatting changes outside the feature-related changed lines are in commits of their own.

[mernst]

Also, these tests fail unless cvc5 is installed:

	 48 - cbmc-incr-smt2-cvc5-CORE (Failed)                 CBMC CORE
	 57 - cbmc-output-file-CORE (Failed)                    CBMC CORE

[tautschnig]

#8214 is to-be-completed work to remove the dependency on CVC5. For Z3, however, we should make clear that this is only needed if you intend to run the test suite. Having Z3 is not a strict build (or operating) requirement.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.77%. Comparing base (f88ea70) to head (6641514).
⚠️ Report is 4 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #9112      +/-   ##
===========================================
- Coverage    80.77%   80.77%   -0.01%     
===========================================
  Files         1712     1712              
  Lines       189814   189814              
  Branches        73       73              
===========================================
- Hits        153328   153325       -3     
- Misses       36486    36489       +3     

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[kroening]

Solaris appears not to have a z3 package