Fix test compilation of test.

  Add test-constraingraph only if dependency to hpp-model-urdf is triggered.

tests/CMakeLists.txt

@@ -47,8 +47,8 @@ MACRO(ADD_TESTCASE NAME GENERATED)
 
 ENDMACRO(ADD_TESTCASE)
 
-ADD_TESTCASE (test-constraintgraph FALSE)
 IF (TEST_UR5)
+  ADD_TESTCASE (test-constraintgraph FALSE)
   SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DTEST_UR5")
   PKG_CONFIG_USE_DEPENDENCY(test-constraintgraph hpp-model-urdf)
 ENDIF ()