[clang] [llvm] [AIX] support builtin_cpu_is() for aix (PR #80069)

[Amy Kwan via cfe-commits]

================
@@ -904,8 +904,17 @@ bool PPCTargetInfo::validateCpuSupports(StringRef FeatureStr) const {
 }
 
 bool PPCTargetInfo::validateCpuIs(StringRef CPUName) const {
+  llvm::Triple Triple = getTriple();
+  if (Triple.isOSLinux()) {
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amy-kwan wrote:

Can if we do something like:
```
if (Triple.isOSAIX()) {
. . . 
}
// Default Linux Behaviour
. . . 
```

https://github.com/llvm/llvm-project/pull/80069