Autoconf, libpq and replacement function

Hi!

I want to use the fnmatch() function in libpq, to support wildcard
certificate matching. This function is part of the standard
(http://www.opengroup.org/onlinepubs/000095399/functions/fnmatch.html),
but obviously not implemented on all platforms (naturally, it's missing
on win32, because that makes life harder..)

Anyway. NetBSD has an implementation of this at
http://cvsweb.netbsd.org/bsdweb.cgi/src/lib/libc/gen/fnmatch.c?rev=1.21&content-type=text/x-cvsweb-markup&only_with_tag=MAIN
that we can "steal" if we need.

How do I make this work with the autoconf magic? I see there is an
AC_CHECK_FNMATCH and AC_REPLACE_FNMATCH and so, but I have a feeling I
need to do something different since it's libpq?

(this might be very obvious how to do, but if it is, please excuse my
extreme autoconf-newbiesm)

//Magnus