uclibc only defines strndup(3) if _GNU_SOURCE is defined

References #516.

src/libimcv/ita/ita_attr_command.c

@@ -13,14 +13,15 @@
  * for more details.
  */
 
+#define _GNU_SOURCE /* for stdndup() */
+#include <string.h>
+
 #include "ita_attr.h"
 #include "ita_attr_command.h"
 
 #include <pen/pen.h>
 #include <utils/debug.h>
 
-#include <string.h>
-
 typedef struct private_ita_attr_command_t private_ita_attr_command_t;
 
 /**