[CIR][CodeGen] `__real` operator on complex rvalue

Minimized test case:
```c++
_Complex A() { __real A(); }
```

Failed assertion:
https://github.com/llvm/clangir/blob/aeac352c9de907fcbb7adde22bbe4a7cfa3105be/clang/lib/CIR/CodeGen/CIRGenExprScalar.cpp#L2066

Flags: `-fclangir -O2 `