test/cmake: add a function for generating unit test targets

Commit 9adedc1f ("test: add new `make` test targets") introduced new
targets for running test-run.py with unit tests. However, this target
doesn't depend on changes in tested libraries and changes in unit tests.
Proposed patch introduces a function that creates a build targets for
unit tests and fixes the described problem with dependencies.

Additionally, patch added missed dependence for popen and popen-child.

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