This fixes the error reported in
https://github.com/llvm/llvm-project/pull/144037.
When computing the aranges table of a CU, LLDB would currently visit all
`DW_TAG_subprogram` DIEs and check their
`DW_AT_low_pc`/`DW_AT_high_pc`/`DW_AT_ranges` attributes. If those don't
exist it would error out and spam the console. Some subprograms
(particularly forward declarations) don't have low/high pc attributes,
so it's not really an "error". See DWARFv5 spec section `3.3.3
Subroutine and Entry Point Locations`:
```
A subroutine entry may have either a DW_AT_low_pc and DW_AT_high_pc
pair of attributes or a DW_AT_ranges attribute whose values encode the
contiguous or non-contiguous address ranges, respectively, of the machine
instructions generated for the subroutine (see Section 2.17 on page 51).
...
A subroutine entry representing a subroutine declaration that is not also a
definition does not have code address or range attributes.
```
We should just ignore those DIEs.
c3ec9e3f65