[clang] [clang] Generate note on declaration for nodiscard-related attributes (PR #112289)

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Sirraide wrote:

> Here the specialization is named, which is potentially helpful.

Hmm, the diagnostic for the error here isn’t particularly great to begin with; I feel like it should instead mention that the return *type*, not the function, is marked `nodiscard`, which might be enough to fix the situation for partial specialisations?

https://github.com/llvm/llvm-project/pull/112289