[llvm] [InstCombine] Evaluate zext nneg as sext where possible (PR #212230)

[Valeriy Savchenko via llvm-commits]

https://github.com/SavchenkoValeriy approved this pull request.

LGTM!
I'd prefer if someone else looks at it before you merge it.
CC @nikic @dtcxzyw 

https://github.com/llvm/llvm-project/pull/212230