[clang] [clang-tools-extra] [Clang] [C2y] Implement N3355 ‘NamedLoops’ (PR #152870)

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Sirraide wrote:

> do we need to update CFG and add tests for named loops with things like reachability diagnostics? And do we need to update anything in the static analyzer for this?

I’m not too familiar w/ the static analyser but I can take a look at the CFG and see if there’s anything to be done there.

https://github.com/llvm/llvm-project/pull/152870