[clang] [C++20][modules] Fix std::initializer_list recognition if it's exported out of a module (PR #118537)

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llvmbot wrote:

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Failed to cherry-pick: 9f1e9f682d0a85ea013ccbce6a3ec4ac1be8335

https://github.com/llvm/llvm-project/actions/runs/12625144536

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/118537