[clang] [Clang] Deleting an incomplete enum type is not an error (PR #118455)

[Alexander Kornienko via cfe-commits]

alexfh wrote:

The test case was reduced to this:
```
template <typename = void> struct a {
  union b {};
  struct c {
    c() { delete d; }
    b *d;
  } f;
};
a e;
```
https://gcc.godbolt.org/z/d5cP4McG3

https://github.com/llvm/llvm-project/pull/118455