[llvm] [hwasan] Add intrinsics for fixed shadow on Aarch64 (PR #89319)

[Thurston Dang via llvm-commits]

thurstond wrote:

> > LGTM up to @fmayer if we need error message on `!.has_value()`
> 
> Yeah, please do that. I don't think it's a good idea to just randomly compile with `0` as shadow address, which I think is unlikely to be correct and will randomly crash at runtime later.

With the latest patch ("_fixed" hwasan check functions), this chunk of code was removed entirely.

https://github.com/llvm/llvm-project/pull/89319