[clang] fix access checking about function overloading (PR #107768)

[Zhikai Zeng via cfe-commits]

Backl1ght wrote:

After some more debugging, I find out that we will check access here at https://github.com/llvm/llvm-project/blob/8e010ac5a173c9dee44b44324169a3e100a1a6fc/clang/lib/Sema/SemaInit.cpp#L7807

And for `f()` inside code below, `Found.getAccess()` is `AS_none` hence `CheckAddressOfMemberAccess` return `AR_accessible` directly.

```cpp
struct Base {
public:
  int f(int);
private:
  int f();  // expect-note {{declared private here}}
};

struct Derived : public Base {};

void f() {
  int(Derived::* public_f)(int) = &Derived::f;
  int(Derived::* private_f)() = &Derived::f;  // expect-error {{'f' is a private member of 'Base'}}
}
```

https://github.com/llvm/llvm-project/pull/107768