gmain: Use alternate signal stack if the application provides one

Some applications, toolkits or languages may define an alternative stack
to use for traces. This is for example the case of go.

So, in case an application defines an alternate signal stack, GLib should
use that instead of the default one to receive signals otherwise it may
break the application expectations and write where it's not allowed to.

glib/gmain.c

@@ -5670,6 +5670,9 @@ ref_unix_signal_handler_unlocked (int signum)
       action.sa_flags = SA_RESTART | SA_NOCLDSTOP;
 #else
       action.sa_flags = SA_NOCLDSTOP;
+#endif
+#ifdef SA_ONSTACK
+      action.sa_flags |= SA_ONSTACK;
 #endif
       sigaction (signum, &action, NULL);
     }