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

[Amy Kwan 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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amy-kwan wrote:

Is it possible for `isOSGlibc()` to return true, but not have access to glibc?
The implementation for this function is as follows:
``` C++
  /// Tests whether the OS uses glibc.
  bool isOSGlibc() const {
    return (getOS() == Triple::Linux || getOS() == Triple::KFreeBSD ||
            getOS() == Triple::Hurd) &&
           !isAndroid();
  }
```
But for example, Alpine Linux doesn't have glibc.

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