Hello bdju, Cuirass can't manage to build kicad¹ also. Comparing to the previous build², libngspice has been updated from version 28 to 34³ and the content of thoses 2 version are drasticly different, so I guess it's the issue. In particular the /gnu/store/...-libngspice-34/include/config.h seems suspicious.
I tried bumping kicad to the latest 5.10, but it didn't make a difference. ¹ https://ci.guix.gnu.org/build/608393/details ² https://ci.guix.gnu.org/build/608201/details ³ https://issues.guix.gnu.org/48979 Cheers, - Brice