[llvm] [AArch64] Reland merge index address with large offset into base address (PR #79951)

[Vitaly Buka via llvm-commits]

vitalybuka wrote:

I don't see how to validate the issue for sure, without rolling back bots to Ubuntu we used at that time.
I did a coupe of runs with your patches on the HEAD, and see no issue.
Let's try to re-land and watch bots.

https://github.com/llvm/llvm-project/pull/79951