It would be nice if SOAAP supported signal handlers

[arichardson]

Low priority issue since most signal handlers are quite simple and I can just analyze them manually, but it would be nice to have.

Ideally SOAAP would look at the function pointers passed to signal() and sigaction() and treat those as reachable functions. For now just treating any function pointer passed there as reachable should be fine, replacement of signal handlers could be omitted for now.

For now adding an annotation to the signal handlers (e.g. __soaap_signal_handler()) would also be fine but then we don't see those set inside other libraries.