[gnome-commander/ConvertWarningsToErrors] Adds format attribute to method definition to suppress suggest-attribute=format warning

[Uwe Scholz <uwescholz src gnome org>]

commit 8cbd9138650201baf279ff960046cfe41d264b87
Author: Uwe Scholz <uwescholz src gnome org>
Date:   Mon Apr 17 15:02:46 2017 +0200

    Adds format attribute to method definition to suppress suggest-attribute=format warning

 src/tags/gnome-cmd-tags.cc |    1 -
 src/tags/gnome-cmd-tags.h  |    7 +++++--
 2 files changed, 5 insertions(+), 3 deletions(-)
---
diff --git a/src/tags/gnome-cmd-tags.cc b/src/tags/gnome-cmd-tags.cc
index e6f3007..1d08955 100644
--- a/src/tags/gnome-cmd-tags.cc
+++ b/src/tags/gnome-cmd-tags.cc
@@ -38,7 +38,6 @@
 
 using namespace std;
 
-
 struct GnomeCmdTagName
 {
     const gchar *name;
diff --git a/src/tags/gnome-cmd-tags.h b/src/tags/gnome-cmd-tags.h
index 6a66066..55239fe 100644
--- a/src/tags/gnome-cmd-tags.h
+++ b/src/tags/gnome-cmd-tags.h
@@ -543,8 +543,11 @@ class GnomeCmdFileMetadata
     void add (const GnomeCmdTag tag, const gchar *value);
     template <typename T>
     void add (const GnomeCmdTag tag, const T &value);
-    void addf (const GnomeCmdTag tag, const gchar *fmt, ...);
-
+#ifdef __GNUC__
+    void addf (const GnomeCmdTag tag, const gchar *fmt, ...) __attribute__ ((format (gnu_printf, 3, 4)));
+#else
+    void addf (const GnomeCmdTag tag, const gchar *fmt, ...)
+#endif
     gboolean has_tag (const GnomeCmdTag tag);
 
     const std::string operator[] (const GnomeCmdTag tag);