Hello, everybody!
I have solved the I/O problem on the DJGPP platform (and fixed some other bugs) and am now uploading a new alpha version of GPC to ftp://agnes.dida.physik.uni-essen.de/gnu-pascal/alpha/ (source (diff) and binaries).
Many thanks to Eli Zaretskii for his help with the I/O problem.
Have fun,
Peter