PX4 Qt Creator

Hello everybody.
I was checking the directories of my PX4 SRC and as I am developing using QTCreator in Linux, there are two directories: Firmware and Firmware-buid.
I have found that during the build process on QTCreator, object files are created inside Firmware-build that are not the ones that will be linked to create the binary that will be loaded on the hardware (or run on SITL).
As example, there is the mc_att_control.cpp.o inside the Firmware-build, but the mc_att_control object that will be used to create the final binary is located inside the Firmware directory, more specifically the build directory/board_name.

Does anyone know what these object files inside Firmware-build are used for?