Remove compiler warnings

[tribad]

With a recent compiler there are still compiler warnings showing up.
To better see if some new things come up, these should be reduced to zero.

[tribad]

Some warnings come from the C-style approaches all over the code.
the offsetof warnings can only be fixed with a re-write of the CON_ code.
Some other things are nasty as well. Where a replacement is easier than some strange rewrite.