[llvm] [llvm][lit] Omit vendor in triples for "native" feature (PR #136325)

[David Spickett via llvm-commits]

https://github.com/DavidSpickett commented:

Sorry for the delay, was busy with dev meeting and so on.

There are some 3 component triples that, if you removed the vendor, would not be compatible with each other. For example `aarch64-amazon-linux` (https://github.com/llvm/llvm-project/pull/136114).

So this is why you are only doing this conversion for 4 element triples, right?

A 4 element triple should have the environment / c library (never quite sure what that bit is) specified. Instead of doing something like implying it from the vendor like `aarch64-amazon-linux` does (for better or worse).

Or in other words, vendor should not change ABI, if the ABI part has been specified already.

Though I wonder why vendor is even a thing, if it has no impact on anything. I guess for fully specified "triples" (quads), that might be expected, but for 3 element triples the vendor would be significant.

If this is your logic, please add that in a comment in the file and in the PR description. That way if we are wrong, it will be easier for someone to state why.

Also if you encountered this through some specific scenario, add that in the PR description. Might help someone who suddenly has more tests running, or not running, after this change.

https://github.com/llvm/llvm-project/pull/136325