[clang] [llvm] [AArch64] Implement GCS ACLE intrinsics (PR #96903)

[John Brawn via cfe-commits]

john-brawn-arm wrote:

> Thanks, LGTM.
> 
> As a follow-up, can you check that the instructions generated from this builtin do inhibit the machine outliner? Maybe all GCS-modifying functions have to inhibit the machine outliner, I'm not 100% sure.

The GCS instructions don't inhibit the machine outliner, but I don't think the machine outliner is a problem. From the perspective of what instructions get executed the only difference when things get outlined is that there's an extra (non-bl) branch instruction, and that won't do anything to the gcs stack.

https://github.com/llvm/llvm-project/pull/96903