[llvm] [Attr] Add `noipa` function attribute (PR #203304)

[Nikita Popov via llvm-commits]

https://github.com/nikic commented:

Submitted https://github.com/llvm/llvm-project/pull/204314 and https://github.com/llvm/llvm-project/pull/204317 for the interposable issues found above.

Looking through more uses of isInterposable(), I think another place that may need adjustment for NoIPA is llvm/lib/Transforms/Utils/Evaluator.cpp (global ctor evaluation).

https://github.com/llvm/llvm-project/pull/203304