The Curtain Wall can trim a regular wall by connecting it.
Select wall & Curtain Wall
Design>Modify Curtain wall>Connect Wall
see note on attached screen shot. As in other areas of archicad when a curve turns back on itself what you are trimming with it may have to be split into two, or else break the curtain wall into appropriate sections.
Erika
Architect, Consultant
MacBook Pro Retina, 15-inch Yosemite 2.8 GHz Intel Core i7 16 GB 1600 MHz DDR3
Mac OSX 10.11.1
AC5-18
Onuma System
"Implementing Successful Building Information Modeling"