[AC 21.5] Update config.guess, config.sub, and install-sh

The Fedora ARM team is trying to roll out aarch64 support. One obstacle they face is that many projects are using > 1 year old versions of config.guess and config.sub, which don't know about that architecture. While there is no guarantee that updating to later versions of those scripts is enough for XEmacs to build and run correctly on the aarch64 platform, it is a necessary first step. I also updated the install-sh script while I was at it.