[clang] [llvm] [Intrinsics][AArch64] Add intrinsic to mask off aliasing vector lanes (PR #117007)

[Sam Tebbs via llvm-commits]

SamTebbs33 wrote:

> If you want to upgrade the whilewr intrinsics (which I think sounds OK to me), then it will need auto-update code something like in https://github.com/llvm/llvm-project/pull/120363/files#diff-0c0305d510a076cef711c006c1d9fd78c95cade1f597d21ee46fd753e6982316. It might be good to separate that out into a separate patch too, to keep things managable.

Thanks for that. I've removed them and am no longer seeing the extra `xtn` instruction that I was before so it looks like those changes are actually unnecessary anyway!

https://github.com/llvm/llvm-project/pull/117007