lang/gprolog: Clean up port (fix build with non-default options)

The no-docs and no-examples options weren't correct. The configuration
value in those causes were no absolute paths as apparently expected, but
relative to STAGEDIR. Fix by letting them install and use post-install
option targets to remove if necessary.

Do other cleanup such as wrap to 80 (when possible) and use options
framework. Also remove option-dependent packagename; that isn't
conventional. Also make configure target generic by platform.