[CMake] ADD_CUSTOM_TARGET USES_TERMINAL not printing out stuff

[Gonzalo Garramuño]

I run cpack with the trick of using a custom configuration.

ADD_CUSTOM_TARGET( bundle
                COMMAND "${CMAKE_CPACK_COMMAND}"
                "-C" "$<CONFIGURATION>"
                "--config" "${CMAKE_BINARY_DIR}/BundleConfig.cmake"
                COMMENT "Running CPack. Please wait..."
                USES_TERMINAL
                DEPENDS translations )

This used to print out all that cpack was doing while it was doing it.  
Now with v3.15.0-rc1 it just sits there and outputs all the text at the 
end when it finishes, which sucks as it looks like it has hung.