OS/400 version V5R3 is not supported by IBM anymore.
In addition, the iSeries system I have here for development has been changed
and the new system is not able to compile for an OS version lower than V6R1.

Thus I made some updates to the libxml2 os400 scripts accordingly:

- Oldest supported OS version is now V6R1.
- Adjust ILE/RPG wrappers comments.
- Update copyright year range.
- Do not log compiler informational messages.