compile: warn on unused return code from Curl_client_write()

lib/curl_setup.h

@@ -643,8 +643,10 @@ int netware_init(void);
 #if defined(__GNUC__) && ((__GNUC__ >= 3) || \
   ((__GNUC__ == 2) && defined(__GNUC_MINOR__) && (__GNUC_MINOR__ >= 7)))
 #  define UNUSED_PARAM __attribute__((__unused__))
+#  define WARN_UNUSED_RESULT __attribute__((warn_unused_result))
 #else
 #  define UNUSED_PARAM /*NOTHING*/
+#  define WARN_UNUSED_RESULT
 #endif
 
 /*

lib/sendf.h

@@ -7,7 +7,7 @@
  *                            | (__| |_| |  _ <| |___
  *                             \___|\___/|_| \_\_____|
  *
- * Copyright (C) 1998 - 2011, Daniel Stenberg, <daniel@haxx.se>, et al.
+ * Copyright (C) 1998 - 2014, Daniel Stenberg, <daniel@haxx.se>, et al.
  *
  * This software is licensed as described in the file COPYING, which
  * you should have received as part of this distribution. The terms
@@ -52,7 +52,7 @@ void Curl_failf(struct SessionHandle *, const char *fmt, ...);
 #define CLIENTWRITE_BOTH   (CLIENTWRITE_BODY|CLIENTWRITE_HEADER)
 
 CURLcode Curl_client_write(struct connectdata *conn, int type, char *ptr,
-                           size_t len);
+                           size_t len) WARN_UNUSED_RESULT;
 
 /* internal read-function, does plain socket only */
 CURLcode Curl_read_plain(curl_socket_t sockfd,