patch 8.2.5137: cannot build without the +channel feature

Problem:    Cannot build without the +channel feature. (Dominique Pellé)
Solution:   Add #ifdef around ch_log() calls. (closes #10598)
diff --git a/src/os_unix.c b/src/os_unix.c
index c0293ce..947f46f 100644
--- a/src/os_unix.c
+++ b/src/os_unix.c
@@ -8323,8 +8323,10 @@
 	timer_created = TRUE;
     }
 
+# ifdef FEAT_JOB_CHANNEL
     ch_log(NULL, "setting timeout timer to %d sec %ld nsec",
 	       (int)interval.it_value.tv_sec, (long)interval.it_value.tv_nsec);
+# endif
     ret = timer_settime(timer_id, 0, &interval, NULL);
     if (ret < 0)
 	semsg(_(e_could_not_set_timeout_str), strerror(errno));