[clang] Performance optimizations for function effects (nonblocking attribute etc.) (PR #96844)

[Doug Wyatt via cfe-commits]

dougsonos wrote:

It would be great if we could merge this soon, please; I'd to start another PR for the 2nd-pass effects analysis and it has a dependency or two on these changes.

https://github.com/llvm/llvm-project/pull/96844