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

[Thorsten Schütt via llvm-commits]

tschuett wrote:

```
def combine_abds : GICombineRule<
  (defs root:$root, build_fn_matchinfo:$matchinfo),
  (match (G_SEXT $lhs, $x),
         (G_SEXT $rhs, $y),
         (G_SUB $sub, $lhs, $rhs),
         (G_ABS $abs, $sub),
         (G_TRUNC $root, $abs):$trunc,
         [{ return Helper.matchAbds(*${trunc}, ${matchinfo}); }]),
  (apply [{ Helper.applyBuildFn(*${trunc}, ${matchinfo}); }])>;
```

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