[clang] [llvm] [AArch64] Codegen for AArch64 Return Address Authentication Hardening (PR #176187)

[Anatoly Trosinenko via cfe-commits]

atrosinenko wrote:

[nit] The code snippet mentioned in the description is one instruction shorter in the latest version:
```
AUTIASP
MOV x0, x30
XPACLRI
LDR w30, [x30]
MOV x30, x0
RET
```

https://github.com/llvm/llvm-project/pull/176187