tor build with rust fails

I tried building tor 0.4.6.5 with rust enabled on NetBSD.

I tried both with BSD make and GNU make, and with cargo's online mode but also with putting the dependencies in a directory manually. Either way, I see:

make all
...
  CC       src/trunnel/libor_trunnel_a-circpad_negotiation.o                                            
  AR       src/trunnel/libor-trunnel.a
  CC       src/lib/trace/trace_stub.o          
  AR       src/lib/libtor-trace.a           
  AR       libtor.a                                 
make[1]: don't know how to make ./src/rust/target/release/libtor_rust.a. Stop                           

Do I manually have to build the rust part first? How? I didn't find any particular instructions for that.