Fixes: #40590
This commit updates gen_app_partitions.py to include only files present
in the current build by extracting the information from the CMake
generated `compile_commands.json` file.
This ensures that object files in sub-projects, such as `empty_cpu0`,
will not be considered by the script.
Using the compile_commands.json instead of walking the whole build tree
for finding object files also improves performance:
Time of executing `gen_app_partitions.py` (Old):
__________________________
Executed in 480.06 millis
usr time 425.83 millis
sys time 49.55 millis
Time of executing `gen_app_partitions.py` (New):
________________________________________________________
Executed in 76.22 millis
usr time 49.00 millis
sys time 24.59 millis
Signed-off-by: Torsten Rasmussen <Torsten.Rasmussen@nordicsemi.no>