Fix rpath under macOS

[volkm]

The test does not run under macOS as libantlr4-runtime.4.7.dylib cannot be found.
Interestingly the problem disappears when running cmake and make a second time.
The following works for me:

mkdir build && cd build
cmake ..
make
./test/carl-parser-test
cmake ..
make
./test/carl-parser-test

The first test fails but the second test is successful.

Apparently the second run of cmake introduces a new rpath target which was not there before:
-Wl,-rpath,~/carl-parser/build/resources/lib

How can we fix the cmake files such that the rpath is already correct the first time?

[tjanson]

This may (or may not) help:

• SO: “How do you add an rpath to an executable in cmake on build (not install) on OSX?”

Also, I think at least some of the macOS CMake rpath settings in CMakeLists.txt are redundant or have no effect since CMP0068 — but I have no idea. It might be worth a look.