[clang] [Clang][AArch64] Add ACLE macros to support Armv9.6 (PR #176755)

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CarolineConcatto wrote:

Hi @aengelke,
I have investigate with our CI and I cannot have a consistent behaviour with instructions count. I cannot reproduce that. 
This PR has nothing different from PR #140591([Clang][AArch64]Add FP8 ACLE macros implementation)
One of the reasons could be the switch statement in `hasFeatures` so I've changed  the switch statement in **AArch64TargetInfo::hasFeature** by having something like:
```
+  if (Feature.starts_with("sve")) {
+    return llvm::StringSwitch<bool>(Feature)
+        .Case("sve", FPU & SveMode)
....
+  // SSVE family: "ssve-..."
+  if (Feature.starts_with("ssve")) {
```
But the results were not very consistent.
This probably needs more investigations in order to reduce the compilation time, because it is nothing very obvious.

https://github.com/llvm/llvm-project/pull/176755