[GSUB/GPOS] Add more buffer messages

Behind HB_BUFFER_MESSAGE_MORE.

https://github.com/harfbuzz/harfbuzz/pull/3495
diff --git a/src/hb-debug.hh b/src/hb-debug.hh
index 3ac7440..905a46a 100644
--- a/src/hb-debug.hh
+++ b/src/hb-debug.hh
@@ -460,4 +460,9 @@
 #endif
 
 
+#ifndef HB_BUFFER_MESSAGE_MORE
+#define HB_BUFFER_MESSAGE_MORE (HB_DEBUG+1)
+#endif
+
+
 #endif /* HB_DEBUG_HH */