[clang] [lldb] [llvm] [AArch64][TargetParser] autogen ArchExtKind enum - renaming (PR #90320)

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ostannard wrote:

@davemgreen This is already split into 18 commits, I don't think there's any reason to split it into 18 PRs, since comments on one of them likely apply to the others.

@tmatheson-arm I don't know if there's any more specific precedent for changing target feature names, but I think this will be a breaking change for existing bitcode files, which we do try to maintain backward compatibility with: https://llvm.org/docs/DeveloperPolicy.html#ir-backwards-compatibility. Maybe we could add IR auto-upgrade code to handle old bitcode?

https://github.com/llvm/llvm-project/pull/90320