Add missing "#include <stddef.h>" to fix the build on macOS

... after 19d7684ca10f.

Prevents:
gateway.c:845:18: error: call to undeclared function 'offsetof'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]

Fixes SF#150.

diff --git a/gateway.c b/gateway.c
index f2cc2ee..7b0412d 100644 (file)
--- a/gateway.c
+++ b/gateway.c
@@ -37,6 +37,7 @@
 #include "config.h"
 
 #include <stdio.h>
+#include <stddef.h>
 #include <sys/types.h>
 
 #ifndef _WIN32