[llvm-branch-commits] [FlowSensitive] [StatusOr] [3/N] support absl::Status ops (PR #163868)

[Florian Mayer via llvm-branch-commits]

https://github.com/fmayer created https://github.com/llvm/llvm-project/pull/163868

`absl::StatusOr::status` allows extraction of the status associated with
a StatusOr value. That can also be used to check whether the StatusOr
has a value or not.

This makes sure code like this is checked properly:

```cpp
int target(absl::StatusOr<int> SOR) {
  if (SOR.status().ok())
    return *SOR;
  return 0;
}
```