Rust platform triples should omit and ignore the vendor

Currently, rust and cargo use the full platform identity for identifying platforms (<arch>-<vendor>-<os>[-<libc]).

However, the vendor attribute in a platform identity (commonly known as platform triples) is a private attribute intended to indicate variants and configurations. For example, RH/Fedora based distros use <arch>-redhat-linux-gnu for the platform identity, Mageia based ones use <arch>-mageia-linux-gnu, and so on. However, for the purposes of determining platform equivalence, only arch, os, and libc matter.

The tooling should be changed to ignore the vendor attribute and platforms should be similarly altered so that the platform triple should only contain the meaningful attributes.

For example, instead of saying x86_64-unknown-linux-gnu, it would be x86_64-linux-gnu. Alternatively, simply forcing the vendor to always be considered something generic (like pc) would be sufficient.

The vendor attribute is meaningful to humans, but not tools.

Start by reviewing how Rust and Cargo represent and compare platform identities, then trace where the vendor attribute affects platform triples. Compare identities that differ only by vendor, such as x86_64-unknown-linux-gnu and x86_64-linux-gnu. Done means equivalent platforms ignore vendor differences and the resulting platform representation contains only meaningful attributes.