patch 9.0.0978: build errors without the +channel feature

Problem:    Build errors without the +channel feature. (John Marriott)
Solution:   Adjust #ifdefs.
diff --git a/src/message.c b/src/message.c
index a2fc008..591691f 100644
--- a/src/message.c
+++ b/src/message.c
@@ -37,7 +37,7 @@
 static char_u	*confirm_msg_tail;		// tail of confirm_msg
 static void display_confirm_msg(void);
 #endif
-#ifdef FEAT_JOB_CHANNEL
+#ifdef FEAT_EVAL
 static int emsg_to_channel_log = FALSE;
 #endif