[OE-core] xz compressed autotools

[Marko Lindqvist]

 I just noticed that xz compressed packages of autotools cannot be
used as that would lead to circular dependency. xz decompressor cannot
be built without autotools.

 Before autoconf-2.69 was released, there was speculation that release
would be provided as tar.xz only. They decided to release at least
2.69 with tar.gz too, but future is not certain.

 I already sent email to autoconf mailing list too, noting that
(currently) OpenEmbedded depends on .tar.gz packages being available,
but maybe that dependency should also be somehow removed from future
OpenEmbedded versions.


 - ML