[clang] [Clang] Warn about `[[noreturn]]` on coroutines (PR #127623)

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Nerixyz wrote:

> Probably where we create the FunctionDecl?

The first warning is emitted when creating the return value. So I'm checking for a coroutine there. To fix the crash in the AnalysisBasedWarnings, I'm checking if a diagnostic with ID 0 would've been emitted.

https://github.com/llvm/llvm-project/pull/127623