* dcrt0.cc (do_exit): Rely on sigproc_terminate to set exit_state

appropriately.
* pinfo.cc (pinfo::exit): Always call sigproc_terminate here.  Rely on
sigproc_terminate to signal signal thread to handle eventual process exit.
* sigproc.cc (no_signals_available): Change criteria for determining if this
process can handle signals to itself.
(my_sendsig): New variable.  Copy of my sendsig handle.
(proc_can_be_signalled): Don't send signals if exit code is set.
(sigproc_terminate): Use and set exit_state appropriately to determine when to
do anything.  Send __SIGEXIT to self to control process exit.
(sig_send): Use my_sendsig for sending signals.  Don't call
proc_can_be_signalled for myself since the criteria is now different for
sending signals to myself.
(wait_sig): Copy myself->sendsig to my_sendsig for future use.  Exit signal
loop when __SIGEXIT is received.  Wait for main thread to exit and use its exit
status to actually exit process.
* sigproc.h (__SIGEXIT): New enum.
* dcrt0.cc (alloc_stack): Eliminate superfluous "return;".
* debug.cc (add_handle): Ditto.
* devices.in (device::parse): Ditto.
* dtable.cc (dtable::vfork_parent_restore): Ditto.
(dtable::vfork_child_fixup): Ditto.
* environ.cc (parse_options): Ditto.
* errno.cc (seterrno_from_win_error): Ditto.
* exceptions.cc (sig_handle_tty_stop): Ditto.
(set_signal_mask): Ditto.
* fhandler.cc (fhandler_base::read): Ditto.
(fhandler_base::operator delete): Ditto.
(fhandler_base::seekdir): Ditto.
(fhandler_base::rewinddir): Ditto.
* fhandler_console.cc (fhandler_console::read): Ditto.
(fhandler_console::fixup_after_exec): Ditto.
* sigproc.cc (sigproc_init): Ditto.
(sigproc_terminate): Ditto.

* devices.cc: Regenerate.

winsup/cygwin/exceptions.cc

@@ -649,7 +649,6 @@ sig_handle_tty_stop (int sig)
       break;
     }
   _my_tls.incyg = 0;
-  return;
 }
 }
 
@@ -1017,7 +1016,6 @@ set_signal_mask (sigset_t newmask, sigset_t& oldmask)
   else
     sigproc_printf ("not calling sig_dispatch_pending");
   mask_sync.release ();
-  return;
 }
 
 int __stdcall