[llvm] [Triple] Add "swift" as a vendor. (PR #85094)

[Fangrui Song via llvm-commits]

https://github.com/MaskRay requested changes to this pull request.

You can freely use a vendor not listed in Triple.h, e.g. you can do `--target=x86_64-swift-linux-gnu` today without any extra code.
Actually, some `VendorType` values are redundant and probably should be there in the first place.
A VendorType member is only needed when it has some special behavior. However, recent Driver improvements try to provide generic mechanisms (e.g. configuration file) to provide customization instead of adding hard-coded logic.

https://github.com/llvm/llvm-project/pull/85094