Where to start with adding a byte compiler warning?

[Ryan C. Thompson]

Hi all,

A while ago, I reported a bug (see below link) requesting that Emacs be 
made to warn if lexical-binding was set as a file-local variable at the 
end of the file, since this causes different behaviour based on how the 
file is loaded. It was suggested that I submit a patch to add it. I 
didn't have time then, but I have time now, so I was wondering if 
someone could point me in the general direction of which file/function I 
should be editing to add this warning so I could get working on it.

Thanks,

-Ryan Thompson

Previous bug report: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=15616