IPv6 support in Cyrus SASL2 distribution

[Xu, Qiang (FXSGSC)]

Hi, all: 

Does SASL2 have buit-in IPv6 support? Or, it needs some options/switches to turn it on/off in compilation?

I searched for the whole distribution (2.1.23), to find the following info:
=======================================================
qxu at gso-linuxcom-01(pts/27):~/opensrc/cyrus-sasl-2.1.23[150]> rgrep "enable-ipv6" "*"
./lib/getaddrinfo.c
 * In the case not using 'configure --enable-ipv6', this getaddrinfo.c
./lib/getnameinfo.c
 * In the case not using 'configure --enable-ipv6', this getnameinfo.c
./saslauthd/getaddrinfo.c
 * In the case not using 'configure --enable-ipv6', this getaddrinfo.c
./saslauthd/getnameinfo.c
 * In the case not using 'configure --enable-ipv6', this getnameinfo.c
=======================================================
It seems there is "enable-ipv6" should be added when the first step of compiling "./configure" is performed. But when I search for the configuration files in the distribution, it doesn't appear in any of them. 

Still, when I try "./configure --enable-ipv6", it doesn't report any error in option's grammar and finishes smoothly: 
=======================================================
qxu at gso-linuxcom-01(pts/27):~/opensrc/cyrus-sasl-2.1.23[152]> ./configure --enable-ipv6
configure: creating cache ./config.cache
...
configure: configuring in saslauthd
configure: running /bin/sh './configure' --prefix=/usr/local  '--enable-ipv6' --cache-file=.././config.cache --srcdir=.
...
configure: creating ./config.status
config.status: creating Makefile
config.status: creating saslauthd.h
config.status: executing depfiles commands
Configuration Complete. Type 'make' to build.
=======================================================
I am a little confused about it. If there is this option, what kind of configuration file should it lie?

So, could anyone tell me is the support for IPv6 built-in or not?

Thanks,
Xu Qiang