[clang] [clang] Don't evaluate the initializer of constexpr-unknown parameters. (PR #142498)

[via cfe-commits]

llvmbot wrote:

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Failed to cherry-pick: 97885213bd4507b204b050c3cd570e365d21cc7d

https://github.com/llvm/llvm-project/actions/runs/15423178980

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/142498