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

[Thurston Dang via llvm-commits]

thurstond wrote:

FYI: I reverted 43ffe2eed0d9f73789dbe213023733d164999306 because of a buildbot breakage (https://github.com/llvm/llvm-project/commit/324b676a3d0449add8d4e24047680125f9b9a716)

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