catkin lib variable for catkin_make and catkin_make_isolated

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Hi, I have two catkin packages, one generating a library and the other makes use of it. In the cmake file of the dependent project, I have "link_directories( ${CATKIN_DEVEL_PREFIX}/lib/ )". This works fine with catkin_make, as the libxxx.so gets generated in devel/lib/. However when using catkin_make_isolated, the libxxx.so gets generated in devel_isolated/project_xxx/lib/ instead. And ${CATKIN_DEVEL_PREFIX} does not seem to dynamically substitute with the correct path according to the catkin command used. What cmake or catkin variable should I use for the link_directories to work in both cases?