Fix dead links in CParser.cs

[throwaway96]

A pair of links in CParser.cs rotted several years ago. One is now a 404, and the other redirects to a spammy domain parking page. I replaced each one with its last valid crawl on archive.org:

• http://www.ssw.uni-linz.ac.at/Coco/C/C.atg: https://web.archive.org/web/20200223191833/http://www.ssw.uni-linz.ac.at/Coco/C/C.atg
• http://flash-gordon.me.uk/ansi.c.txt: https://web.archive.org/web/20170605121212/http://flash-gordon.me.uk/ansi.c.txt