[BUG] Builds against upstream czmq(v4) fail valgrind tests

[jimklimov]

This project has a czmq4 branch set up to test compilations against both our current standard fork of czmq-v3.0.2 and the upstream czmq4. Builds of the latter fail with many "definitely leaked" entries in valgrind, see e.g. https://travis-ci.org/jimklimov/fty-metric-composite/builds/236341368 and https://travis-ci.org/jimklimov/fty-metric-composite/builds/236341368 in particular.

This is a blocker for updating the baseline of 42ity project to use only the maintained upstream czmq.

As can be seen in the comparison at https://github.com/42ity/fty-metric-composite/compare/master...czmq4?expand=1 there is no C/C++ codebase change in the branch, just added recipes to try both CZMQ versions in different runs.

[jimklimov]

Fixed by zeromq/czmq#1675