[llvm] Triple: Fix handling of macos with unexpected target arches (PR #75469)

[Chris B via llvm-commits]

https://github.com/llvm-beanz approved this pull request.

I think this is the correct change, but I'm sure Apple has some out-of-tree code that will likely be impacted.

cc: @lhames, @dsandersllvm, @rudkx. Apologies I don't know Aditya, or Charu's GitHub accounts and the autocomplete is failing me.

https://github.com/llvm/llvm-project/pull/75469