[zeromq-dev] cmake subdir support in zproject

[Arnaud Loonstra]

Hey all,

I've created a PR for issue 
https://github.com/zeromq/zproject/issues/1237 
(https://github.com/zeromq/zproject/issues/1238)

When a zproject generated project is used as a subdirectory in another 
cmake project it will fail. This is due to custom targets being defined 
in the cmake file. (i.e. clang-format-*, distclean and selftest 
targets). We can skip these definitions when they already exist and this 
fixes the issue.

However I can't oversee the consequences fully so if anybody has 
feedback on this fix/workaround please make some noise.

Rg,

Arnaud