[llvm] [SCEV] Fix incorrect NUW inference (PR #70521)

[Nikita Popov via llvm-commits]

nikic wrote:

Is the problem here that the nuw flag is just entirely incorrect, or that it is correct at that use, but we set it on the addrec in general? If the latter, would it be possible to just not set the addrec flag? That is, make the code `if (AR->hasNoUnsignedWrap() || canProveNUW())` and drop the addrec flag manipulation code?

https://github.com/llvm/llvm-project/pull/70521