The gprolog configure script appears to ignore the exec-prefix
information handed to it which indicates where compiled binaries
should be installed. It insists on installing everything into
/usr/gprolog-$VERSION/ and then creating symlinks in /usr/bin.

This script will correct this by moving the files in
/usr/gprolog-$VERSION to their proper places in /usr,
ie: binaries are placed in /usr/bin, libraries in /usr/lib or
/usr/lib64 and documentation in /usr/doc/gprolog-$VERSION.