I think that those are just references to source files that they have managed to find. If you look in the .rodata sections of any disassembled actor you can usually find a text string that refers to the name of original source file. So if you were hoping to find actual source code... sorry to burst your bubble but you probably won't find anything.
As for compiling things for the N64, I made a (semi-complete) tutorial on writing hacks in C with mips-gcc-- you should check it out. If you're talking about actually making ROMs, you might have some luck talking to Vexiant, xdaniel, or marshallh about that.
I am the ocean Lit by the flame I am the mountain Peace is my name I am the river Touched by the wind I am the story I never end.