[CMake] set INSTALL_RPATH for python on linux

To avoid the need to set `LD_LIBRARY_PATH` when the
`CMAKE_INSTALL_PREFIX` is not a standard one.

src/dynamic_graph/CMakeLists.txt

-# Copyright 2010-2020, Florent Lamiraux, Thomas Moulard, Olivier Stasse, Guilhem Saurel, JRL, CNRS/AIST, LAAS-CNRS
+# Copyright 2010-2021, Florent Lamiraux, Thomas Moulard, Olivier Stasse, Guilhem Saurel, JRL, CNRS/AIST, LAAS-CNRS
 
 SET(PYTHON_MODULE wrap)
 
@@ -17,6 +17,10 @@ TARGET_LINK_BOOST_PYTHON(${PYTHON_MODULE} PRIVATE)
 # Remove prefix lib
 SET_TARGET_PROPERTIES(${PYTHON_MODULE} PROPERTIES PREFIX "")
 
+IF(UNIX AND NOT APPLE)
+  SET_TARGET_PROPERTIES(${PYTHON_MODULE} PROPERTIES INSTALL_RPATH "\$ORIGIN/../../..")
+ENDIF()
+
 INSTALL(TARGETS ${PYTHON_MODULE}
   EXPORT ${TARGETS_EXPORT_NAME}
   DESTINATION ${PYTHON_SITELIB}/dynamic_graph)