CVS HEAD is broken by flex

I found CVS HEAD is broken and the following error is reported.
My environment is RHEL4 Update 2 x86_64 with gcc 3.4.4 and flex 2.5.33.

In file included from ../../../src/include/port.h:17,
from ../../../src/include/c.h:841,
from ../../../src/include/postgres_fe.h:21,
from psqlscan.l:40:
/usr/include/netdb.h:560: error: syntax error before '[' token
make[3]: *** [psqlscan.o] Error 1
make[3]: *** Waiting for unfinished jobs....
make[2]: *** [all] Error 2
make[1]: *** [all] Error 2
make: *** [all] Error 2

The suspect is flex (or yy template file). It defines "__unused" to
be empty, but netdb.h uses "__unused" as a variable.
I found a similar case from google.
http://mailman.icsi.berkeley.edu/pipermail/xorp-cvs/2007-March/009928.html

[src/bin/psql/psqlscan.c]
9 #if defined(__FreeBSD__)
10 #include <sys/cdefs.h>
11 #else
-> 12 #define __unused
13 #endif

[/usr/include/netdb.h]
552 struct gaicb
553 {
554 const char *ar_name; /* Name to look up. */
555 const char *ar_service; /* Service name. */
556 const struct addrinfo *ar_request; /* Additional request specification. */
557 struct addrinfo *ar_result; /* Pointer to result. */
558 /* The following are internal elements. */
559 int __return;
-> 560 int __unused[5];
561 };

Here is a brute fix for the problem, but it is probably improper.
What is better way to fix?

Index: src/include/port.h
===================================================================
--- src/include/port.h (HEAD)
+++ src/include/port.h (working copy)
@@ -13,6 +13,7 @@
#ifndef PG_PORT_H
#define PG_PORT_H

+#undef __unused
#include <ctype.h>
#include <netdb.h>
#include <pwd.h>

Regards,
---
ITAGAKI Takahiro
NTT Open Source Software Center