ok, got it too compile... as you said, it was commented, stupid me.
when i run the plugin i get:
root@bela:~/Bela/projects/jalv-Bela/build# ./jalv http://gareus.org/oss/lv2/fat1
Plugin: http://gareus.org/oss/lv2/fat1
UI: None
Plugin requires 1 inputs and 1 outputs
Sample rate: 44100 Hz
Block length: 64 frames
MIDI buffers: 4096 bytes
Comm buffers: 65536 bytes
Update rate: 25.0 Hz
Illegal instruction
and it aborts. not sure if the binary i installed is the reason for this. will try to compile the fat1.lv2 from source to see if it makes a difference