Fix for yet another compilation failure on Windows which was introduced during

work on WL#2787 "Add view definer/owner to the view definition (.frm) to check
privileges on used tables and stored routines when using a VIEW."
(aka bug #13402 "Windows VS 2003 Compiler error")


sql/mysqld.cc:
  handle_connections_namedpipes():
    THD::host member has moved to the Security_context class.
    New THD::security_ctx member points to active security context.

sql/mysqld.cc

@@ -4016,8 +4016,8 @@ extern "C" pthread_handler_decl(handle_connections_namedpipes,arg)
       delete thd;
       continue;
     }
-    /* host name is unknown */
-    thd->host = my_strdup(my_localhost,MYF(0)); /* Host is unknown */
+    /* Host is unknown */
+    thd->security_ctx->host= my_strdup(my_localhost, MYF(0));
     create_new_thread(thd);
   }