Modify -DCMAKE_INSTALL_RPATH for MacOS

[yuzie007]

Thank you so much developers for sharing the code, which helps me quite a lot for jumping into ML-potential researches!

Short description

This modification allows us to use pacemaker also in MacOS.

Long description

When I installed pyace in MacOS and tried to use pacemaker, I got the following error message;

% pacemaker -t
Traceback (most recent call last):
  File "/Users/ikeda/miniconda3/envs/myenv/bin/pacemaker", line 26, in <module>
    from pyace.generalfit import GeneralACEFit
  File "/Users/ikeda/miniconda3/envs/myenv/lib/python3.10/site-packages/pyace/__init__.py", line 9, in <module>
    from pyace.asecalc import PyACECalculator, PyACEEnsembleCalculator
  File "/Users/ikeda/miniconda3/envs/myenv/lib/python3.10/site-packages/pyace/asecalc.py", line 7, in <module>
    from pyace.basis import ACEBBasisSet, ACECTildeBasisSet, BBasisConfiguration
ImportError: dlopen(/Users/ikeda/miniconda3/envs/myenv/lib/python3.10/site-packages/pyace/basis.cpython-310-darwin.so, 0x0002): Library not loaded: @rpath/libyaml-cpp-pace.0.6.dylib
  Referenced from: <525B2942-D3A8-351C-8B10-03BD3B9A7E08> /Users/ikeda/miniconda3/envs/myenv/lib/python3.10/site-packages/pyace/basis.cpython-310-darwin.so
  Reason: tried: '$ORIGIN/libyaml-cpp-pace.0.6.dylib' (no such file), '$ORIGIN/libyaml-cpp-pace.0.6.dylib' (no such file), '/Users/ikeda/miniconda3/envs/myenv/bin/../lib/libyaml-cpp-pace.0.6.dylib' (no such file), '/Users/ikeda/miniconda3/envs/myenv/bin/../lib/libyaml-cpp-pace.0.6.dylib' (no such file), '/System/Volumes/Preboot/Cryptexes/OS@rpath/libyaml-cpp-pace.0.6.dylib' (no such file), '$ORIGIN/libyaml-cpp-pace.0.6.dylib' (no such file), '$ORIGIN/libyaml-cpp-pace.0.6.dylib' (no such file), '/Users/ikeda/miniconda3/envs/myenv/bin/../lib/libyaml-cpp-pace.0.6.dylib' (no such file), '/Users/ikeda/miniconda3/envs/myenv/bin/../lib/libyaml-cpp-pace.0.6.dylib' (no such file), '/usr/local/lib/libyaml-cpp-pace.0.6.dylib' (no such file), '/usr/lib/libyaml-cpp-pace.0.6.dylib' (no such file, not in dyld cache)

In a Linux system, I did not get the error above.

After a bit of surveys and trials, I realized that giving @loader_path instead of $ORIGIN to CMAKE_INSTALL_RPATH in setup.py (or maybe equivalently in CMakeLists.txt) for MacOS solves the issue.

I am honestly not very familiar with cmake and pybind11 and cannot tell clearly why the above worked, but this may be not super unreasonable (https://stackoverflow.com/q/53428219).