[clang] [llvm] [PowerPC][X86] Make cpu id builtins target independent and lower for PPC (PR #68919)

[Fangrui Song via cfe-commits]

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@@ -359,6 +359,13 @@ class LLVM_LIBRARY_VISIBILITY PPCTargetInfo : public TargetInfo {
   bool isSPRegName(StringRef RegName) const override {
     return RegName.equals("r1") || RegName.equals("x1");
   }
+
+  // We support __builtin_cpu_supports/__builtin_cpu_is on targets that
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MaskRay wrote:

Linux musl also supports `AT_HWCAP` `AT_HWCAP2`.

https://github.com/llvm/llvm-project/pull/68919