Include config.h in files that test for constants defined in it.

diff --git a/dlls/winsock/socket.c b/dlls/winsock/socket.c
index f49c2d0..6aaeb27 100644
--- a/dlls/winsock/socket.c
+++ b/dlls/winsock/socket.c
@@ -17,6 +17,7 @@
  
 #include "config.h"
 
+#include <stdio.h>
 #include <string.h>
 #include <sys/types.h>
 #ifdef HAVE_SYS_IPC_H