CMake: Improve support to build python bindings

[marbre]

• Refactors iree_pybind_cc_library()
• Adds iree_py_extension()
• Updates and CMake targets for python bindings

The bindings are still not complete and currently only implements support for Linux.

Depends on #693 and #694. I will drop these commits and rebase if these patches get merged separately into master.

[marbre]

I am gladly awaiting your feedback :) We might need an iteration before this can be merged, but I hope it is the right step to enable building the python bindings with CMake.

[stellaraccident]

Looking now...

[GMNGeoffrey]

This broke the cmake build. To run kokoro on PRs and ensure we avoid a breakage, a repository collaborator needs to tag the PR with "kokoro:run"

[stellaraccident]

TIL Ok - sorry about that. I assumed the presubmits were authoritative...

…

On Thu, Feb 6, 2020 at 1:12 PM Geoffrey Martin-Noble < ***@***.***> wrote: This broke the cmake build. To run kokoro on PRs and ensure we avoid a breakage, a repository collaborator needs to tag the PR with "kokoro:run" — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#695>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AADYVAE537HNI7XMJ3KNS3TRBR4NFANCNFSM4KRCQWYQ> .

[GMNGeoffrey]

Yeah it's not a great situation :-/ They are somewhat authoritative, but we have to give them permission to run for contributions from outside the organization and nothing blocks on them on import. That's why I wanted to use GitHub required checks because it gives you a nice UI that indicates "hey this isn't ready to merge", but unfortunately it breaks copybara's ability to push directly to master.

[ScottTodd]

CI build fix is at #700. We also discussed ways to make "this hasn't run presubmits yet" blocking or more obvious, but don't yet have a concrete plan.

[marbre]

My apologies. I probably have missed to do a full rebuild and only checked if the incremental build succeeds. Will send a patch to fix the bindings.