[clang] More fixes for P3144R2 implementation (PR #149406)

[Harald van Dijk via cfe-commits]

hvdijk wrote:

How about this? For an incomplete class C, we used to generate the misleading "cannot delete pointer to incomplete type 'C'", now "cannot delete pointer to incomplete class 'C'", for a pointer to void, matching wording can just be "cannot delete pointer to 'void'". Does that look acceptable?

It's possible to merge err_delete_incomplete and err_delete_void_ptr_operand as you suggested but I think that requires a bit more complexity in err_delete_incomplete, or accepting misleading diagnostics.

https://github.com/llvm/llvm-project/pull/149406