reinstate z3 package from @Drup with a stable release

[c-cube]

Trying to resurrect the package for Z3 and its OCaml bindings.

Previously:

• Add Z3 package #3298 (addition)
• Revert "Add Z3 package" #4217 (removal)

Licensing problems should be gone, since Z3 is now under MIT. I added a package for the last release and the dev-repo field.

[camelus]

✅ All lint checks passed 894b545

• These packages passed lint tests: Z3.4.5.0

---

✅ Installability check (7787 → 7788)

• new installable packages (1): Z3.4.5.0

[c-cube]

I don't get why the datakit tests fail so fast, and I don't know how to access the error files to check why…

[c-cube]

Not sure what's wrong exactly…

[kit-ty-kate]

On MacOS X, Travis fails with:

#=== ERROR while installing Z3.4.5.0 ==========================================#
Some files in ~/.opam/system/install/Z3.install couldn't be installed:
  - /Users/travis/.opam/system/build/Z3.4.5.0/build/libz3.so to /Users/travis/.opam/system/lib/Z3

[c-cube]

Ah, yeah, the .install written by @Drup might be linux-specific :-(
But there are also weird failures on some specific linux distributions

[Drup]

Did you try to get rid of that ? I feel like this is not really acceptable if it gets into opam's main repository.

[avsm]

It would be good to get rid of this, indeed. Why is it needed?

[Drup]

At the time, it was needed because the package recompile Z3 entirely, Z3's build system was complicated and because I'm not very good at C(++) linking rules.
Now, I think it would be better to rely on system-provided .so/.h files, but it needs modifying Z3's build system or just plain extracting the OCaml part, and building it outside.
opam's LLVM package does the former, so I guess it works.

[c-cube]

modifying Z3's build system? :-/
this sounds super awful…

[gasche]

Ping. Do we have a chance to have a nice solution this time around? (I think many people would be interested in having an easy way to use Z3 using opam.) If not, we may want to close the PR.

[c-cube]

Sorry I haven't updated this. I don't know of a solution that would be simple enough (building manually seems a bit too scary, especially when Z3 maintainers themselves are moving to cmake).

So I'm closing this until a better, cleaner solution is found…