variant.h or variant.cpp file for DUE to assign PC20

_From @castfxman on January 19, 2016 20:15_

I have an Arduino DUE based board and need to have PC20 on the SAM3X8E chip go to one of my motors. This was done by DigiX for a board based on the DUE and I am trying to do the same thing but just with one pin. I don't know if I should be rewriting the variant.h file or variant.cpp file in the Hardware\arduino\sam\variants\arduino_due_x section. Any help would be appreciated so I don't have to just print the board differently. Thank you in advance!

_Copied from original issue: arduino/Arduino#4455_

The request names Hardware\arduino\sam\variants\arduino_due_x\variant.h and variant.cpp. Start by inspecting how the Arduino Due variant maps SAM3X8E pins, then determine which file controls PC20 exposure. Done should establish whether PC20 can be assigned to the motor without changing the board design.

Written by the indexing model from the issue text.