[clang] AArch64 Tablegen Update (PR #179692)

[David Spickett via cfe-commits]

DavidSpickett wrote:

Please resolve the merge conflict and tell me what commands you used to compare the files.

I think the header guard change is fine, and actually is what I would expect from a file with that name in fact. However, I'd like to double check myself locally that there isn't anything else changing.

https://github.com/llvm/llvm-project/pull/179692