[clang] [clang][ASTImporter] Link FunctionDecl into its DeclContext before importing its body (PR #214009)

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guillem-bartrina-sonarsource wrote:

I see that an LLDB test started failing: https://github.com/llvm/llvm-project/actions/runs/31012683468/job/92328750113?pr=214009#step:3:14210.

If amending this test is not an option, we can approach the fix differently. Similar to how we detect function decl cycles, we can do the same for var decls.

https://github.com/llvm/llvm-project/pull/214009