add_library(scopedA INTERFACE IMPORTED)
set_property(TARGET scopedA PROPERTY INTERFACE_COMPILE_DEFINITIONS "SCOPED_A_2")

add_library(scope2_iface INTERFACE)
set_property(TARGET scope2_iface PROPERTY INTERFACE_COMPILE_DEFINITIONS
  "$<TARGET_PROPERTY:scopedA,INTERFACE_COMPILE_DEFINITIONS>"
  )
set_property(TARGET scope2_iface PROPERTY CUSTOM_PROP
  "$<TARGET_PROPERTY:scopedA,INTERFACE_COMPILE_DEFINITIONS>"
  )