update third_party/{snappy,xz}/config.{guess,sub} based on upstream

[grooverdan]

From 'http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.guess;hb=HEAD' and 'http://git.savannah.gnu.org/gitweb/?p=config.git;a=blob_plain;f=config.sub;hb=HEAD'

To get PerconaFT to compile on ppc64 I needed a newer version of these third party stubs. Copied identically as of a few days ago and hence SPDX-License-Identifier: GPL-3.0 WITH Autoconf-exception-2.0 rather than BSD-2.