[clang] [llvm] [AArch64][Driver] Allow runtime detection to override default features. (PR #176340)

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llvmbot wrote:

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Failed to cherry-pick: 9458d2a0f403f4e79130da56b74d7828867f332c

https://github.com/llvm/llvm-project/actions/runs/21205398410

Please manually backport the fix and push it to your github fork.  Once this is done, please create a [pull request](https://github.com/llvm/llvm-project/compare)

https://github.com/llvm/llvm-project/pull/176340