[clang] [clang][ThreadSafety] Instantiate a parameter's attribute naming a later parameter (PR #232784)

[Jameson Nash via cfe-commits]

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+// Under -fexperimental-late-parse-attributes, an attribute on a parameter may
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vtjnash wrote:

They could. And IIRC, I had asked Claude the same question, and it pointed out that this functionality only works with `-fexperimental-late-parse-attributes`, so it would likely add a lot of line noise for each case to need to specify the conflicting late vs early expected results for every line.

https://github.com/llvm/llvm-project/pull/232784