New Custom Library

I am trying to add new Custom Libraries into the ArduPIlot. So I added all the files to the Libraries folder and then imported all the Libraries from GCS_MAVlink.h. But when I build it for SITL it shows these errors:

ArduPlane/GCS_Mavlink.cpp.22.o: In function GCS_MAVLINK_Plane::handleMessage(__mavlink_message*)': GCS_Mavlink.cpp:(.text._ZN17GCS_MAVLINK_Plane13handleMessageEP17__mavlink_message+0x3dd): undefined reference towc_InitRng’
GCS_Mavlink.cpp:(.text._ZN17GCS_MAVLINK_Plane13handleMessageEP17__mavlink_message+0x3ec): undefined reference to wc_InitRsaKey' GCS_Mavlink.cpp:(.text._ZN17GCS_MAVLINK_Plane13handleMessageEP17__mavlink_message+0x408): undefined reference towc_MakeRsaKey’
collect2: error: ld returned 1 exit status

Any Idea on how to solve it? There are other people with the same question, on how to add a custom library to ardupilot. But those are also unanswered. Basically to sum up , my question is how to add external Libraries to ardupilot?