Fix warnings

[maxime-esa]

The following warnings should be fixed in the runtime:

po_hi_transport.c:457:66: warning: unused parameter 'task_id' [-Wunused-parameter]
po_hi_transport.c:457:90: warning: unused parameter 'port' [-Wunused-parameter]
po_hi_transport.c:526:73: warning: unused parameter 'src' [-Wunused-parameter]
po_hi_transport.c:526:99: warning: unused parameter 'dst' [-Wunused-parameter]
po_hi_transport.c:539: 100: warning: unused parameter 'p' [-Wunused-parameter]

po_hi_semaphore.c:39:107: warning: unused parameter 'id' [-Wunused-parameter]

po_hi_task.c:483:40: warning: cast between incompatible function types from 'void * ()(void)' to 'void * ()(void )' [-Wcast-function-type]
err = pthread_create (&tid, &attr, (void ()(void))start_routine, arg);
^
And these in the generated code:

activity.c : variable "error" is set but not used

[yoogx]

Closing, this ticket is addressed by OpenAADL/ocarina#268