how to add prebuilt object files to executable in cmake

Question

I have an add_custom_target that triggers a make for a project (that project does not use cmake!) and generates an object file. I would like to add this object

Answer 1

SET(OBJS
  ${CMAKE_CURRENT_SOURCE_DIR}/libs/obj.o
)

ADD_EXECUTABLE(myProgram ${OBJS} )

SET_SOURCE_FILES_PROPERTIES(
  ${OBJS}
  PROPERTIES
  EXTERNAL_OBJECT true
  GENERATED true
)

That worked for me. Apparently one must set these two properties, EXTERNAL_OBJECT and GENERATED.