test-rfifolock and test-vmstate only build on POSIX hosts.  Exclude them
if building for Windows.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: NStefan Weil <sw@weilnetz.de>
Signed-off-by: NAndreas Färber <afaerber@suse.de>