compiling cyrus-imapd on amd64

[David Newman]

cyrus-imapd-2.3.12p2, FreeBSD 7.0 64-bit, Opteron CPUs

When building from source, running configure produces this error:

checking build system type... Invalid configuration
`amd64-unknown-freebsd7.0': machine `amd64-unknown' not recognized

Searching archives showed some posts from a few years ago asking if
autoconf and automake are installed (they are).

Is cyrus-imapd supported on 64-bit amd machines? If so, what steps are
needed to compile it?

thanks

dn