[gnome-software] trivial: Fix a compile warning with clang

[Richard Hughes <rhughes src gnome org>]

commit 6ed979398b658a0771d5dc7a0d917b58c939052c
Author: Richard Hughes <richard hughsie com>
Date:   Tue Oct 8 12:08:46 2013 +0100

    trivial: Fix a compile warning with clang

 src/plugins/appstream-app.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)
---
diff --git a/src/plugins/appstream-app.c b/src/plugins/appstream-app.c
index 47f2449..ee818fd 100644
--- a/src/plugins/appstream-app.c
+++ b/src/plugins/appstream-app.c
@@ -21,6 +21,9 @@
 
 #include "config.h"
 
+#define _GNU_SOURCE
+#include <string.h>
+
 #include "appstream-app.h"
 #include "appstream-common.h"