Make LIB_NDOF define part of the targets interface

indra/cmake/NDOF.cmake

@@ -24,13 +24,11 @@ if (NDOF)
     elseif (DARWIN OR LINUX)
       set_target_libraries( ndof::ndof ndofdev)
     endif (WINDOWS)
-    set(NDOF_FOUND 1)
+    target_compile_definitions( ndof::ndof INTERFACE LIB_NDOF=1)
   endif (USESYSTEMLIBS)
 endif (NDOF)
 
-if (NDOF_FOUND)
-  add_definitions(-DLIB_NDOF=1)
-else (NDOF_FOUND)
+if (NOT NDOF_FOUND)
   message(STATUS "Building without N-DoF joystick support")
-endif (NDOF_FOUND)
+endif ()