[glib] Make gtk-doc handle GLogField

[Matthias Clasen <matthiasc src gnome org>]

commit 65540860705f747586369757b9cfb790428a7baf
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Jul 20 19:42:52 2016 -0400

    Make gtk-doc handle GLogField
    
    gtk-doc can't deal with typedef struct {...} GLogField, it seems.

 glib/gmessages.h |    5 +++--
 1 files changed, 3 insertions(+), 2 deletions(-)
---
diff --git a/glib/gmessages.h b/glib/gmessages.h
index 7471e4e..5cbdad7 100644
--- a/glib/gmessages.h
+++ b/glib/gmessages.h
@@ -152,12 +152,13 @@ typedef enum
  *
  * Since: 2.50
  */
-typedef struct
+typedef struct _GLogField GLogField;
+struct _GLogField
 {
   const gchar *key;
   gconstpointer value;
   gssize length;
-} GLogField;
+};
 
 /**
  * GLogWriterFunc: