[llvm] [GlobalISel] Add G_ABDS and G_ABDU instructions (PR #118122)

[Thorsten Schütt via llvm-commits]

tschuett wrote:

RISCV lowering:
// abds(lhs, rhs) -> sub(smax(lhs,rhs), smin(lhs,rhs))
// abdu(lhs, rhs) -> sub(umax(lhs,rhs), umin(lhs,rhs))

https://github.com/llvm/llvm-project/pull/118122