Install the SASL library to build the VNC SASL auth protocol code.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200309122454.22551-3-philmd@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>