[gnome-commander/ConvertWarningsToErrors] gnome-cmd-xml-config.h: fix -Wimplicit-fallthrough

[Uwe Scholz <uwescholz src gnome org>]

commit d748ed40ff6e66991aa2d9575731736c6fa4a0da
Author: Mamoru TASAKA <mtasaka fedoraproject org>
Date:   Sun Apr 23 12:21:10 2017 +0900

    gnome-cmd-xml-config.h: fix -Wimplicit-fallthrough
    
    src/gnome-cmd-xml-config.h:201:23: error: this statement may fall through [-Werror=implicit-fallthrough=]

 src/gnome-cmd-xml-config.h |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/gnome-cmd-xml-config.h b/src/gnome-cmd-xml-config.h
index 9858557..2f79865 100644
--- a/src/gnome-cmd-xml-config.h
+++ b/src/gnome-cmd-xml-config.h
@@ -200,6 +200,9 @@ namespace XML
                 case stateAttribute:
                     s << '"';
 
+#if defined (__GNUC__) && __GNUC__ >= 7
+                __attribute__ ((fallthrough));
+#endif
                 case stateTagName:
                 case stateTag:
                     if (self_closed)