Ignore unwinding edges when checking for unconditional recursion
The unconditional recursion lint determines if all execution paths
eventually lead to a self-recursive call.
The implementation always follows unwinding edges which limits its
practical utility. For example, it would not lint function `f` because a
call to `g` might unwind. It also wouldn't lint function `h` because an
overflow check preceding the self-recursive call might unwind:
```rust
pub fn f() {
g();
f();
}
pub fn g() { /* ... */ }
pub fn h(a: usize) {
h(a + 1);
}
```
To avoid the issue, assume that terminators that might continue
execution along non-unwinding edges do so.
Fixes#78474.
21b4a9cfdc