[llvm] [Support] Redefine endianness::native (PR #67876)

[Markus Böck via llvm-commits]

https://github.com/zero9178 approved this pull request.

LGTM! I do not see the point of `endianness::native` being a distinct value either. Please wait a few days (probably best until after the weekend) before landing this to give others a chance to review as well.

Are there any plans to also remove `system_endianness()`? It seems entirely equivalent to just using `llvm::support::native`.
Simiar possible follow cleanup is that `llvm::HashBuilder` is now entirely equivalent to just using `llvm::HashBuilderImpl` directly.  

https://github.com/llvm/llvm-project/pull/67876