Please read the GPC Manual (info files or other formats) as well as the README and BUGS files that come with GPC (usually installed in directory /usr/local/doc/gpc), plus other docs that might help (the DJGPP FAQ if you use DJGPP, etc.) before you send email to the maintainers or mailing list.
In particular, the BUGS file contains information on how to submit bug reports in the most efficient way.
The Support chapter of the GPC Manual tells you where to find more information about GPC and how to contact the GPC developers. (see Support)