postprocess: CustomTarget_signing: find libs in INSTDIR
postprocess: CustomTarget_signing: find libs in INSTDIR

... not sure if it wouldn't be better to do this directly when linking,
but what do i know about this signing stuff anyway...

Change-Id: Iabebf21dd8c0198afb4fd03403fca3ca8a0c9b22

JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core,JurassicWordExcel/core