[clang] [llvm] [AArch64][clang][llvm] Add ACLE `stshh` atomic store builtin (PR #181386)

[Kerry McLaughlin via cfe-commits]

https://github.com/kmclaughlin-arm approved this pull request.

Hi @jthackray, I just have a few more minor comments but otherwise this LGTM

https://github.com/llvm/llvm-project/pull/181386