[clang] [clang] Add break/continue stmts with missing lable to the AST (PR #168332)

[via cfe-commits]

Sirraide wrote:

> because trying to evaluate e.g. `int f() { break; }` would definitely crash.

As would
```c++
constexpr int f() {
  switch (1) {
    case 1: continue a;
  }
  return 1;
}
```

https://github.com/llvm/llvm-project/pull/168332