[CMake] C header file cross dependency

[Wagner Martin]

Hi @all,

I've finally found a solution to the problem.

My solution is here: https://github.com/martinwag/test_cmake/tree/master

What I did:
- remove  "OBJECT" library targets as they do not work in combination with interface libraries
- added one install target per library, so I get one "lib*.a" archive per library (which is not what I need)
- added an post install target as described here: stackoverflow.com/questions/9998679 . This step creates a "thin" archive, that is packed with the other archives at cpack-time. This archive can be used as single file when linking in the consuming stage.

Regards,
Martin