tests/CMakeLists.txt uses target_sources but says it works with CMake 2.8.1

[fove-robin]

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Issue description

tests/CMakeLists.txt uses CMake's target_sources, which was only added in CMake 3.1.
cmake_minimum_required is set to 2.8.1 in that file, and 2.8.12 in the project root.

This is causing libzmq project's Jenkins to fail:
https://libzmq.cloudapp.net/job/libzmq/1820/console

Note Jenkins isn't reporting the problem, but it's not exactly working either...

Environment

• libzmq version (commit hash if unreleased): d5e4319
• OS: all
• CMake: before v3.1

Minimal test code / Steps to reproduce the issue

1. kick off CI on Jenkins

What's the actual result? (include assertion message & call stack if applicable)

CMake Error at tests/CMakeLists.txt:184 (target_sources):
  Unknown CMake command "target_sources".

What's the expected result?

Jenkins should build, not just flake out and say "SUCCESS!" (Fixing Jenkins itself is a separate issue I guess...?)

[bluca]

Not sure where the Jenkins script actually is unfortunately.

Any idea how to do the same CMake thing without target_sources?

[bluca]

Well it looks like those directives are not actually needed - testing without them right now

[bluca]

Sigh it looks like it's necessary on Windows, not on *nix

[bluca]

I have a different solution - a bit clunkier but it seems to work