[CMake] eigenpy is required at runtime

If libeigenpy.so is available at buildtime, and not at runtime, the
python bindings can't work.

CMakeLists.txt

@@ -38,7 +38,7 @@ ADD_REQUIRED_DEPENDENCY("pinocchio >= 2.0.0")
 SET(BOOST_COMPONENTS unit_test_framework serialization)
 
 IF(BUILD_PYTHON_INTERFACE)
-  ADD_COMPILE_DEPENDENCY("eigenpy >= 1.3.1")
+  ADD_REQUIRED_DEPENDENCY("eigenpy >= 1.3.1")
   SET(BOOST_COMPONENTS ${BOOST_COMPONENTS} python)
   FINDPYTHON()
   INCLUDE_DIRECTORIES(SYSTEM ${PYTHON_INCLUDE_DIRS})