The buildfaq.pdf is a document about FPC and Lazarus building, and in particular cross-compiling. It is the successor of the 1.0.x period make cycle FAQ, and is maintained by an FPC core development member (Marco).
The document is in LyX because it allows easy offline editing and good printing quality. It is a hyperlinked PDF, but when the notoriously difficult conversion of LaTeX to HTML allows it, a HTML version is also generated. Diagrams are made with DIA, and then exported to PNG. The source files are in SVN in fpcdocs/buildfaq, but if you want changes, please don't commit directly but do it via Marco. Thanks.