[clang] nonblocking/nonallocating attributes: 2nd pass caller/callee analysis (PR #99656)

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Sirraide wrote:

> First, thank you so much @Sirraide for doing such a thorough review here! I've been buried lately, so knowing you were taking care of this was really appreciated!

Np. I also reviewed the first effects pr before this one, so I figured it’d make sense for me to review this because I was already familiar w/ the rest of the implementation.

https://github.com/llvm/llvm-project/pull/99656