Use correct type for saved signal handler

A user noticed that the sim assigns the result of a call to 'signal'
to a variable like:

  RETSIGTYPE (*prev_sigint) ();

However, it's more correct to use (int) here.

This patch fixes the error.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=32466
Approved-By: Andrew Burgess <aburgess@redhat.com>
3 files changed