[llvm] [ConstraintElim] Add tests for llvm.abs >= 0 (PR #79068)

[Alexander Shaposhnikov via llvm-commits]

alexander-shaposhnikov wrote:

@fhahn - the accompanying PR is https://github.com/llvm/llvm-project/pull/79070 - is it OK to land it too ? 

https://github.com/llvm/llvm-project/pull/79068