It does not matter if you use su or sudo. In tdelibs CMakeLists.txt DEFAULT_SUPER_USER_COMMAND is not set to a short name "su" or "sudo", but the name with the full path - ie. "/bin/su". And this is then the reason for this warning.

I rebuilt tdelibs and tdebase with the proposed patches. I did not modify my configure options. The error message no longer appears. Please push the patches to git. :-)

Thank you and good work!

Darrell