The test-filter-{mirror,redirector} cases use socketpair() API that
is only available on POSIX and should only be built for POSIX.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20220925113032.1949844-30-bmeng.cn@gmail.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>