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

[Alexander Yermolovich via llvm-commits]

ayermolo wrote:

> > Maybe an extra test to capture when DIEs have the same offsets?
> 
> Do you have any suggestions on how to create this situation? It seems hard to control the offset of DIEs for tests that start from `.ll` inputs 🤔

Two TUs with similar structure should have the same relative offsets.
Something like:
clang++ -g2 -gpubnames -fdebug-types-section main.cpp 
```
struct Foo {
  char f1;
};
struct Foo2 {
  char f2;
};

Foo fooGlobal;
Foo2 foo2Global;
```

```
Name 4 {
      Hash: 0x7C952063
      String: 0x0000005d "char"
      Entry @ 0xcc {
        Abbrev: 0x48c
        Tag: DW_TAG_base_type
        DW_IDX_type_unit: 0x00
        DW_IDX_die_offset: 0x00000033
      }
      Entry @ 0xd3 {
        Abbrev: 0x48c
        Tag: DW_TAG_base_type
        DW_IDX_type_unit: 0x01
        DW_IDX_die_offset: 0x00000033
      }
    }
```


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