[llvm] [DWARF] Disable generation of cross-CU references for DWARF V2 (PR #192516)

[via llvm-commits]

Nadharm wrote:

Made some additional changes to test files in latest commit

cross-cu-no-ref-addr-dwarf-v2.ll:
- UNSUPPORTED: target=powerpc64{{.*}}-aix{{.*}}
- CHECK DWARF version
- match on DIE offset/address

debug-loc-offset.ll:
- DW_FORM_ref_addr -> DW_FORM_ref4 and side-effects

ref_addr_relocation.ll:
- removed dwarf v2 RUN and checks

sections_as_references.ll:
- use dwarf v3 instead

https://github.com/llvm/llvm-project/pull/192516