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)

src/regexp_bt.c

@@ -3163,8 +3163,10 @@ bt_did_time_out(int *timed_out)
     {
 	if (timed_out != NULL)
 	{
+# ifdef FEAT_JOB_CHANNEL
 	    if (!*timed_out)
 		ch_log(NULL, "BT regexp timed out");
+# endif
 	    *timed_out = TRUE;
 	}
 	return TRUE;