[llvm] Add target-byteorder for cases where endian in target triple is what matters (PR #107915)

[James Henderson via llvm-commits]

https://github.com/jh7370 approved this pull request.

Thanks. I'm "approving" this, to clear my "needs changes", but somebody who understands the original test should actually still review it.

https://github.com/llvm/llvm-project/pull/107915