Platform encountered on was ~amd64 Gentoo Linux. This is a bug in the klibc package, not necessarily Gentoo. Copied handling of '-D' argument, changed to '--param', problem solved. Will include patch ...
Created attachment 180213 [details, diff] patch to allow klcc to parse '--param' options
Patch doesn't work as described in 1st post, decided to go be more correct in implementation at last second, putting it alongside '-include', rebuilt to confirm working; problem solved.