[llvm] [DWARFVerifier] Fix debug_str_offsets DWARF version detection (PR #81303)

[Felipe de Azevedo Piovezan via llvm-commits]

felipepiovezan wrote:

@dwblaikie please see the two last paragraphs of the commit message, as they are new.
Sadly the test we had originally never worked as intended :( 

https://github.com/llvm/llvm-project/pull/81303