Switch to target_link_libraries. (#92)

This allows us to hide more of the libraries from downstream
consumers.

While we are in here, do slight cleanups so it is more clear
which libraries are depended on.

Signed-off-by: Chris Lalancette <clalancette@gmail.com>

CMakeLists.txt

@@ -24,10 +24,18 @@ target_include_directories(laser_geometry
     $<INSTALL_INTERFACE:include/${PROJECT_NAME}>
   ${Eigen3_INCLUDE_DIRS}
 )
-ament_target_dependencies(laser_geometry
-  "rclcpp"
-  "sensor_msgs"
-  "tf2"
+target_link_libraries(laser_geometry PUBLIC
+  ${sensor_msgs_TARGETS}
+  tf2::tf2
+)
+if(TARGET Eigen3::Eigen)
+  target_link_libraries(laser_geometry PUBLIC Eigen3::Eigen)
+else()
+  target_include_directories(laser_geometry PUBLIC ${Eigen3_INCLUDE_DIRS})
+endif()
+
+target_link_libraries(laser_geometry PRIVATE
+  rclcpp::rclcpp
 )
 
 # Causes the visibility macros to use dllexport rather than dllimport,
@@ -42,9 +50,7 @@ ament_export_libraries(laser_geometry)
 ament_export_targets(laser_geometry)
 
 ament_export_dependencies(
-  eigen3_cmake_module
   Eigen3
-  rclcpp
   sensor_msgs
   tf2
 )
@@ -80,7 +86,7 @@ if(BUILD_TESTING)
     test/projection_test.cpp
     TIMEOUT 240)
   if(TARGET projection_test)
-    target_link_libraries(projection_test laser_geometry)
+    target_link_libraries(projection_test laser_geometry rclcpp::rclcpp)
   endif()
 
   # Python test