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/proto.h b/src/proto.h
index 4c7f8c9..9d1e134 100644
--- a/src/proto.h
+++ b/src/proto.h
@@ -263,11 +263,12 @@
 # ifdef FEAT_JOB_CHANNEL
 #  include "job.pro"
 #  include "channel.pro"
+# endif
 
+# ifdef FEAT_EVAL
 // Not generated automatically so that we can add an extra attribute.
 void ch_log(channel_T *ch, const char *fmt, ...) ATTRIBUTE_FORMAT_PRINTF(2, 3);
 void ch_error(channel_T *ch, const char *fmt, ...) ATTRIBUTE_FORMAT_PRINTF(2, 3);
-
 # endif
 
 # if defined(FEAT_GUI) || defined(FEAT_JOB_CHANNEL)