[clang] [llvm] [PowerPC] Add builtin_cpu_is P11 support (PR #99550)

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llvmbot wrote:

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>/cherry-pick https://github.com/llvm/llvm-project/commit/63b382bbde5994e8f2cec75883320e3ad9fd618f

Error: Command failed due to missing milestone.

https://github.com/llvm/llvm-project/pull/99550