On The debian-legal mailing list there currently is a major discussion about the "freeness" of the "GNU Free Documentation License". You may want to look at the archives yourself, one point to start is
http://lists.debian.org/debian-legal/2003/debian-legal-200304/msg00307.html
The problem are the "Invariant Sections" of the GFDL, which make the GFDL non-free from Debian's viewpoint. Looking at gpc's documentation, I see the GFDL-1.1 (with the short example GFDL license at the end), but in the man page I only find:
COPYING Copyright (c) 1997-2003 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.1 version published by the Free Software Foundation.
A copy of the GFDL comes as a texinfo document along with the GPC manual.
In contrast with copying-fdl.texi, there is no mentioning of the "Invariant Sections":
"If you have no Invariant Sections, write ``with no Invariant Sections'' instead of saying which ones are invariant. If you have no Front-Cover Texts, write ``no Front-Cover Texts'' instead of ``Front-Cover Texts being @var{list}''; likewise for Back-Cover Texts."
Please clarify the copyright of the man page. I'll have to remove the info and html docs from the Debian main section (maybe somebody volunteers to repackage them to the non-free section), but to keep at least the manual pages in the package I'd like to see the license of the manual pages be clarified.
Thanks, Matthias