[clang] [llvm] Reland [clang][AArch64] Add getHostCPUFeatures to query for enabled f… (PR #115467)

[Sjoerd Meijer via cfe-commits]

https://github.com/sjoerdmeijer approved this pull request.

Looks like a good fix to me. 
Please wait a day in case @davemgreen has comments, and it is better to commit in the morning anyway. :)

For convenience, the diff with the previous version is this first line in the test:

 ```
// REQUIRES: aarch64-registered-target,system-linux,host-arch-compatible
```

And this in the lit config file:

```
if config.host_arch in config.target_triple:
    config.available_features.add("host-arch-compatible")
```

https://github.com/llvm/llvm-project/pull/115467