[ddp-actuator-solver] Add link to the qpOASES library

The ddp-actuator-solver depends on the qpOASES library which was not linked to the plugin in the CMakeLists. 

src/CMakeLists.txt

@@ -108,6 +108,10 @@ FOREACH(plugin ${plugins})
   PKG_CONFIG_USE_DEPENDENCY(${LIBRARY_NAME} pinocchio)
 
   IF(DDP_ACTUATOR_SOLVER_FOUND)
+    SET(CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake/find-external/qpOASES")
+    FIND_PACKAGE("qpOASES" REQUIRED)
+    INCLUDE_DIRECTORIES(SYSTEM ${qpOASES_INCLUDE_DIRS})
+    TARGET_LINK_LIBRARIES(${LIBRARY_NAME} ${qpOASES_LIBRARIES})
     PKG_CONFIG_USE_DEPENDENCY(${LIBRARY_NAME} ddp-actuator-solver )
   ENDIF(DDP_ACTUATOR_SOLVER_FOUND)