Ensure orocos-kdl is available as a target (#10)

orocos_kdl_vendor/orocos_kdl_vendor-extras.cmake

@@ -12,15 +12,22 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+find_package(orocos_kdl REQUIRED)
+if(NOT TARGET orocos-kdl)
+  find_library(orocos_kdl_LIBRARY orocos-kdl REQUIRED)
+  add_library(orocos-kdl SHARED IMPORTED)
+  set_target_properties(orocos-kdl PROPERTIES
+    IMPORTED_LOCATION ${orocos_kdl_LIBRARY}
+    INTERFACE_LINK_LIBRARIES ${orocos_kdl_LIBRARIES}
+    INTERFACE_INCLUDE_DIRECTORIES ${orocos_kdl_INCLUDE_DIRS})
+endif()
+
 find_package(eigen3_cmake_module REQUIRED)
 find_package(Eigen3 REQUIRED)
-find_package(orocos_kdl REQUIRED)
-if(TARGET orocos-kdl)
-  message(STATUS "Ensuring Eigen3 include directory is part of orocos-kdl CMake target")
-  if(TARGET Eigen3::Eigen)
-    # TODO: require target to exist when https://github.com/ros2/choco-packages/issues/19 is addressed
-    target_link_libraries(orocos-kdl INTERFACE Eigen3::Eigen)
-  else()
-    target_include_directories(orocos-kdl SYSTEM INTERFACE ${Eigen3_INCLUDE_DIRS})
-  endif()
+message(STATUS "Ensuring Eigen3 include directory is part of orocos-kdl CMake target")
+if(TARGET Eigen3::Eigen)
+  # TODO: require target to exist when https://github.com/ros2/choco-packages/issues/19 is addressed
+  target_link_libraries(orocos-kdl INTERFACE Eigen3::Eigen)
+else()
+  target_include_directories(orocos-kdl SYSTEM INTERFACE ${Eigen3_INCLUDE_DIRS})
 endif()