[ClangImporter] Fix Build Break Due to `clang` API changes (#84925)
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https://github.com/swiftlang/llvm-project/pull/11631 is cherry-picking
`clang` commits that change `CompilerInstance`'s APIs. The API changes
are causing Swift build breaks. This PR fixes the API breaks.
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Co-authored-by: Jan Svoboda <jan@svoboda.ai>