[llvm] [LFI][AArch64] Add AArch64 LFI rewrites for system instructions (PR #186896)

[Zachary Yedidia via llvm-commits]

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zyedidia wrote:

Sounds good. I have reduced the doc changes and kept the name the same. I'll move the documentation in a separate PR.

https://github.com/llvm/llvm-project/pull/186896