Use CMAKE_DL_LIBS CMake library to link library that provides dlopen

[traversaro]

CMake provides the CMAKE_DL_LIBS variable that contain the library that contains dlopen and dlclose.

Using it, it is possible to avoid to hardcode any platform specific logic, for existing platform and for future platforms, that will just need to set the CMAKE_DL_LIBS in their CMake platform file.

[traversaro]

In ROS2 the CMAKE_DL_LIBS variable is already used in https://github.com/ros2/rcutils/blob/5.0.1/CMakeLists.txt#L133 .