This segfault is present all the way back to Itcl 4.0b6 (May 2011).

It's not a regression due to recent developments.

Trying to go back further gets into sources that no longer compile
against released Tcl 8.6 (interfaces changed).

itcl::widget is not a command in Itcl 3.  There's no legacy interest
in getting this right.

It appears to be an experiment or work-in-progress that just
never got successfully completed.

Letting it sit at low prio for now.