avoid -Wsign-compare warning in argv copying
diff --git a/sshd.c b/sshd.c
index 2ff3855..0e3ac26 100644
--- a/sshd.c
+++ b/sshd.c
@@ -1383,7 +1383,7 @@
 	saved_argc = ac;
 	rexec_argc = ac;
 	saved_argv = xcalloc(ac + 1, sizeof(*saved_argv));
-	for (i = 0; i < ac; i++)
+	for (i = 0; (int)i < ac; i++)
 		saved_argv[i] = xstrdup(av[i]);
 	saved_argv[i] = NULL;