horst: Fix build for LEDE

Fortified headers don't seem to like _GNU_SOURCE in this case,
but we can remove that define since it's not needed. Add a patch
for LEDE until a new horst version is released.

Signed-off-by: Bruno Randolf <br1@einfach.org>

net/horst/patches/0001-Remove-_GNU_SOURCE-from-ccan-config.patch

@@ -0,0 +1,26 @@
+From c91e2f6d72823938052044eef858c3c675617ae4 Mon Sep 17 00:00:00 2001
+From: Bruno Randolf <br1@einfach.org>
+Date: Wed, 15 Mar 2017 21:22:48 +0000
+Subject: [PATCH] Remove _GNU_SOURCE from ccan config
+
+It creates problems with LEDEs FORTIFY and is not needed
+---
+ config.h | 3 ---
+ 1 file changed, 3 deletions(-)
+
+diff --git a/config.h b/config.h
+index 5c398c4..7e1027a 100644
+--- a/config.h
++++ b/config.h
+@@ -1,8 +1,5 @@
+ /* Generated by CCAN configurator */
+ #ifndef CCAN_CONFIG_H
+ #define CCAN_CONFIG_H
+-#ifndef _GNU_SOURCE
+-#define _GNU_SOURCE /* Always use GNU extensions. */
+-#endif
+ #define HAVE_TYPEOF 1
+ #endif /* CCAN_CONFIG_H */
+-- 
+2.7.4
+