[llvm] [DAG] Add legalization handling for ABDS/ABDU (PR #92576)

[via llvm-commits]

bgra8 wrote:

@RKSimon here's the repro for completion:

`repro.cc`:

```cxx
extern "C" int abs(int);
struct a {
  a();
  int m_fn1() { return b; }
  int b : 4;
};
int c;
void cg() {
  a ci, cj;
  int ck = ci.m_fn1(), cl = cj.m_fn1();
  if (abs(ck - cl) <= c)
    a();
}
```

compilation command:
```
$ clang -c -O1 repro.cc -o /tmp/out
```

https://github.com/llvm/llvm-project/pull/92576