[clang] [clang][analyzer] Ignore unnamed bitfields in UninitializedObjectChecker (PR #132427)

[via cfe-commits]

YLChenZ wrote:

My proposal is to judge the current `FieldDecl` at the beginning of the loop, and if it's a UnamedBitField, just skip it, because at that point the UnamedBitField's static check should be passing. If it's a NamedBitField then it needs to be initialized to pass the static check (i.e. go deeper to determine the type, value or whatever).
```cpp
for (const FieldDecl *I : RD->fields()) {
    if (I->isUnnamedBitField()) {   //my proposal 
      continue;                              
    }
    ......
    if (isPrimitiveType(T)) {
        // Skip unnamed bitfields (padding)
        if (I->isUnnamedBitField()) {   //his proposal 
            continue;
        }
        ......
    }
}
```

The current test cases are sufficient. I'm not sure about the answers to the other questions.

https://github.com/llvm/llvm-project/pull/132427