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

[Alastair Houghton via llvm-commits]

al45tair wrote:

An example from one of the PRs I have open against Swift: https://github.com/apple/swift/pull/71844/files#diff-f768ac8c03b01ed7761b76d70eaa046bd6032a4b7559873d13fd46a5033c9e83

(There are others, I think, in various parts of the code.)

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