[clang] [C23] Fix typeof handling in enum declarations (PR #146394)

[via cfe-commits]

Sirraide wrote:

> let's handle C++ separately to keep the patch reasonable?

~~What about Objective-C then?~~

```c
void f() {
    ^ typeof((void)0) {}; // Ok
    ^ typeof(void) {};    // Error but should probably be ok
}
```

But yeah, doing all of that in this pr might be too much—unless the changes you’ve already made happen to already fix these cases.

https://github.com/llvm/llvm-project/pull/146394