Replace SIGIO with SIGRTMIN to support multiple events
Replace SIGIO with SIGRTMIN to support multiple events

We know that:
- realtime uses SIGRTMIN+3
- PAPI uses SIGRTMIN+2

so SIGRTMIN+4 is a safe bet (temporarily)
HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit,HPCToolkit/hpctoolkit