In file included from src/core/or/connection_edge.c:70:0:
./src/core/or/circuitpadding.h:16:26: error: redefinition of typedef ‘circuit_t’
./src/core/or/or.h:930:26: note: previous declaration of ‘circuit_t’ was here
./src/core/or/circuitpadding.h:17:33: error: redefinition of typedef ‘origin_circuit_t’
./src/core/or/or.h:931:33: note: previous declaration of ‘origin_circuit_t’ was here
./src/core/or/circuitpadding.h:18:23: error: redefinition of typedef ‘cell_t’
./src/core/or/or.h:628:23: note: previous declaration of ‘cell_t’ was here

typedef doesn't work for forward declarations, but plain struct
without a typedef wrapper does (and unlike the _t type aliases makes
it clearer for everyone whether you're talking about the struct or
the pointer).