[llvm] [GlobalISel] Add G_ABS computeKnownBits (PR #154413)

[Pragyansh Chaturvedi via llvm-commits]

r41k0u wrote:

My bad, I was only checking on some arches. Did a full build for all tests, and have updated the AMDGPU ones

https://github.com/llvm/llvm-project/pull/154413