CI fails on jobs using Z3 4.8.11

[RyanGlScott]

Currently, all CI jobs which use Z3 4.8.11 will fail when running the expr-builder-smtlib2 test suite. Here is an example:

Test suite expr-builder-smtlib2: RUNNING...
SOLVER SELF-REPORTED VERSIONS::
  Solver cvc4 -> This is CVC4 version 1.8
  Solver yices -> Yices 2.6.4
  Solver z3 -> Z3 version 4.8.11 - 64 bit
Tests
  <snip>
  Z3 string1:                              OK (unexpected: unicode and string escaping not supported for older Z3 versions; upgrade to at least 4.8.12) (0.02s)
     (unexpected success: unicode and string escaping not supported for older Z3 versions; upgrade to at least 4.8.12)
    Use -p '/Z3 string1/' to rerun this test only.
  Z3 string2:                              OK (0.04s)
  Z3 string3:                              OK (unexpected: unicode and string escaping not supported for older Z3 versions; upgrade to at least 4.8.12) (0.17s)
     (unexpected success: unicode and string escaping not supported for older Z3 versions; upgrade to at least 4.8.12)
    Use -p '/Z3 string3/' to rerun this test only.
  Z3 string4:                              OK (unexpected: unicode and string escaping not supported for older Z3 versions; upgrade to at least 4.8.12) (1.19s)
     (unexpected success: unicode and string escaping not supported for older Z3 versions; upgrade to at least 4.8.12)
    Use -p '/Z3 string4/' to rerun this test only.
  Z3 string5:                              OK (unexpected: unicode and string escaping not supported for older Z3 versions; upgrade to at least 4.8.12) (0.04s)
     (unexpected success: unicode and string escaping not supported for older Z3 versions; upgrade to at least 4.8.12)
    Use -p '/Z3 string5/' to rerun this test only.
  <snip>

4 out of 70 tests failed (7.11s)
Test suite expr-builder-smtlib2: FAIL

#180 contains a fix for this issue, but it is currently being held up on other things. I think it would be worth isolating the change to only run these tests on Z3 4.8.12 or later for the sake of fixing the CI in the short term.

[robdockins]

I believe this is fixed now.