[llvm] [InstCombine] Regard zext nneg as sext when folding add(zext neg(add)) (PR #88887)

[via llvm-commits]

ZelinMa557 wrote:

Hi, I have added the test and proof according to https://llvm.org/docs/InstCombineContributorGuide.html, can you take a look when it is convenient for you? @XChy @nikic @dtcxzyw 

https://github.com/llvm/llvm-project/pull/88887