Fix SIGCHLD handler prototype for GCC 15+ default C23.

Bug: https://bugs.gentoo.org/943773

--- a/main.c
+++ b/main.c
@@ -427,8 +427,9 @@
 	return 1;
 }

-void child_sigchld()
+void child_sigchld(int sig)
 {
+	(void)sig;
 	if ( getppid() != 1 )
 		return;

@@ -437,7 +438,7 @@ void child_sigchld()
 	return;
 }

-int sethandler_sigchld ( void ( *handler ) () )
+int sethandler_sigchld ( void ( *handler ) (int) )
 {
 	struct sigaction sa;
 	sa.sa_handler = handler;