(gud-gdb-marker-filter): Include "\n" in regexp

to detect the beginning of a level 2 or 3 annotation.

lisp/progmodes/gud.el

@@ -477,7 +477,7 @@ off the specialized speedbar mode."
     ;; gud-marker-acc until we receive the rest of it.	Since we
     ;; know the full marker regexp above failed, it's pretty simple to
     ;; test for marker starts.
-    (if (string-match "\032.*\\'" gud-marker-acc)
+    (if (string-match "\n\\(\032.*\\)?\\'" gud-marker-acc)
 	(progn
 	  ;; Everything before the potential marker start can be output.
 	  (setq output (concat output (substring gud-marker-acc