[llvm] [AsmPrinter][DebugNames] Implement DW_IDX_parent entries (PR #77457)

[Greg Clayton via llvm-commits]

clayborg wrote:

One question: This won't cause a forward declaration to show up in the .debug_names will it? I was thinking about this scenario, not sure if it can happen, but:
```
class A { // Forward decl only for 'A'
  class B { // full definition for class 'B'
  ...
  };
};
```
I want to make sure that if we enable this, it is fine to have an accelerator entry for `class A`, but it shouldn't be included in the name lookup if `class A` is just a forward declaration. We will need to point to an entry for `class A` for in the parent index in the entry for `class B`, but we shouldn't have a name entry for `class A` as we don't want to try and lookup this class and find a class that is only a declaration.

https://github.com/llvm/llvm-project/pull/77457