Platformio build is failing

ESP-32 target has `platformio.ini` file that is Platformio project file, i assuming it should be possible to build project using Platformio.

Currently build if failing due to the way Platformio places build artifacts in the same output folder

Error is blow:
```
*** Multiple ways to build the same target were specified for: /media/dronische/storage/prj/esp32-cspot/esp32-cspot/targets/esp32/.pio/build/cspot-wrover-b/bitstream.o (from ['/media/dronische/storage/prj/esp32-cspot/esp32-cspot/cspot/bell/libhelix-mp3/bitstream.c'] and from ['/media/dronische/storage/prj/esp32-cspot/esp32-cspot/cspot/bell/libhelix-aac/bitstream.c'])
File "/home/dronische/.platformio/platforms/espressif32/builder/frameworks/espidf.py", line 620, in compile_source_files
```

Clearly `bitstream.c` is inluded in 2 different dependency repos: `/cspot/bell/libhelix-aac` and `/cspot/bell/libhelix-mp3` that suppose to produce the same output `/cspot-wrover-b/bitstream.o`

I guess it shoud be adressed in the `bell` repo.