This is not an arduino source code file. It contains machine specific registers so it will only run on the processor it was designed to run on what ever that is.
The line :-#define FOSC 12000000L
Suggests a 12MHz crystal, an arduino has a 16MHz one so all the baud rate timings will be off.
Do you want it to run on an arduino?
If so the best bet is to simply copy it into a window in the arduino environment and try and compile it, which it won't but then try and work through the errors. Better still write it from scratch using the arduino DMX library.