[clang] [llvm] [clang][DebugInfo] Add symbol for debugger with VTable information. (PR #130255)

[Carlos Alberto Enciso via llvm-commits]

CarlosAlbertoEnciso wrote:

> > Given the _vtable$ artificial member: use the DW_AT_containing_type to find the vtable global variable.
> 
> It seems to me that this attribute should refer to a type and not a variable.

Good point. Another option is to use `DW_AT_specification`. 
```
0x00000042:   DW_TAG_variable
                DW_AT_specification (0x0000005c "_vtable$")
                DW_AT_linkage_name  ("_ZTV8CDerived")
                ...

0x0000004c:   DW_TAG_structure_type ("CDerived")
                ...
0x0000005c:     DW_TAG_variable
                  DW_AT_name  ("_vtable$")
                  DW_AT_artificial  (true)
                  DW_AT_specification <0x00000042>  --> VTable global variable
                  ...
```
But potentially consumers can go into a loop if they follow both `DW_AT_specification`, without having additional knowledge about the `artificial` DIE.
```
0x00000042:   DW_TAG_variable
                DW_AT_linkage_name  ("_ZTV8CDerived")
                ...

0x0000004c:   DW_TAG_structure_type ("CDerived")
                ...
0x0000005c:     DW_TAG_variable
                  DW_AT_name  ("_vtable$")
                  DW_AT_artificial  (true)
                  DW_AT_specification <0x00000042>  --> VTable global variable
                  ...
```
If we remove the first `DW_AT_specification`, we lost the ability to traverse the global variables (vtable's) and find their associated compound type.

https://github.com/llvm/llvm-project/pull/130255