CMake warnings under OS X: MACOSX_RPATH is not specified for the following targets

Adding set(CMAKE_MACOSX_RPATH 1) into CMakeLists.txt, before the above written statements, lets the warnings disappear. The linking problem after executing make stays. This brings me to the assumption that my RPATH setup has nothing to do with my linking problem.

Nevertheless, this thread's problem is solved. An explanation about the correct use of the RPATH options inside CMakeLists.txt is still very welcome!

Well, I'll just go one step forward from @fotinsky's answer. (Feel free to incorporate this into your answer.)

The output of the warning's suggestion to run cmake-policy --help-policy CMP0042 is:

CMake 2.8.12 and newer has support for using ``@rpath`` in a target's install
name.  This was enabled by setting the target property
``MACOSX_RPATH``.  The ``@rpath`` in an install name is a more
flexible and powerful mechanism than ``@executable_path`` or ``@loader_path``
for locating shared libraries.

CMake 3.0 and later prefer this property to be ON by default.  Projects
wanting ``@rpath`` in a target's install name may remove any setting of
the ``INSTALL_NAME_DIR`` and ``CMAKE_INSTALL_NAME_DIR``
variables.

This policy was introduced in CMake version 3.0.  CMake version
3.1.3 warns when the policy is not set and uses OLD behavior.  Use
the cmake_policy command to set it to OLD or NEW explicitly.

This simply means that in later cmake versions, the user is required to explicitly enable or disable CMAKE_MACOSX_RPATH.

There's also more background info on the introduction of this variable in this CMake blog entry.