If the system has GTK but not libvte, it's more helpful to
tell the user that libvte is missing than to simply say that
GTK is not present.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 1374162121-31582-1-git-send-email-peter.maydell@linaro.org
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>