[clang] [analyzer] Discard non-live source frames from the current stack (PR #213779)

[Benedek Kaibas via cfe-commits]

benedekaibas wrote:

> @benedekaibas Can you post an example FP html finding here? I could maybe reproduce and create a test case for you in the background.

[report-3efbc2.html](https://github.com/user-attachments/files/30700407/report-3efbc2.html)

In the meantime I could reproduce the error. As a note for the AI policy, after my implementation of the test case that triggered the FP I asked AI to ask me questions which would help me to reduce the number of lines since I had a pretty long test case. This code snippet is the result of that refactor:

```
namespace repro {
struct PunnedPointer {
  unsigned char Data[sizeof(void *)];
  PunnedPointer(long V = 0) { *this = V; }
  PunnedPointer &operator=(long V) {
    __builtin_memcpy(Data, &V, sizeof(Data));
    return *this;
  }
};
} // namespace repro

struct PointerUnion {
  repro::PunnedPointer Val;
  PointerUnion(const int *V) { Val = reinterpret_cast<long>(V); }
};

void foo(PointerUnion arg);

void no_dangling_by_value_argument() {
  int local = 0;
  foo(&local); // no-warning
}
```

https://github.com/llvm/llvm-project/pull/213779