macOS: fix symlink origin
Should match "BUNDLE DESTINATION" from CMAKE_INSTALL_DESTINATION_ARGS. "../MacOS/CMake" works for the in-build symlink, but will not in general for the installed symlink.
Should match "BUNDLE DESTINATION" from CMAKE_INSTALL_DESTINATION_ARGS. "../MacOS/CMake" works for the in-build symlink, but will not in general for the installed symlink.