[gtksourceview] Add comment about an alternative to gtksourcetypes.h in C11

[Sébastien Wilmet <swilmet src gnome org>]

commit 391f247e5454960044573422002816de702b4ce2
Author: Sébastien Wilmet <swilmet gnome org>
Date:   Fri Oct 14 20:35:40 2016 +0200

    Add comment about an alternative to gtksourcetypes.h in C11
    
    https://bugzilla.gnome.org/show_bug.cgi?id=679424

 gtksourceview/gtksourcetypes.h |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)
---
diff --git a/gtksourceview/gtksourcetypes.h b/gtksourceview/gtksourcetypes.h
index ee3efe2..ddc7426 100644
--- a/gtksourceview/gtksourcetypes.h
+++ b/gtksourceview/gtksourcetypes.h
@@ -35,6 +35,12 @@
 
 G_BEGIN_DECLS
 
+/* This header exists to avoid cycles in header inclusions, when header A needs
+ * the type B and header B needs the type A. For an alternative way to solve
+ * this problem (in C11), see:
+ * https://bugzilla.gnome.org/show_bug.cgi?id=679424#c20
+ */
+
 typedef struct _GtkSourceBuffer                        GtkSourceBuffer;
 typedef struct _GtkSourceCompletionContext     GtkSourceCompletionContext;
 typedef struct _GtkSourceCompletion            GtkSourceCompletion;