configure: Drop ancient Solaris 9 and earlier support

Solaris 9 was released in 2002, its successor Solaris 10 was
released in 2005, and Solaris 9 was end-of-lifed in 2014.
Nobody has stepped forward to express interest in supporting
Solaris of any flavour, so removing support for the ancient
versions seems uncontroversial.

In particular, this allows us to remove a use of 'uname'
in configure that won't work if you're cross-compiling.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Daniel P. Berrange <berrange@redhat.com>
Message-id: 1499955697-28045-1-git-send-email-peter.maydell@linaro.org