[DWARF] Corrected behavior for when no .apple_names section is present in the object.

The verifier should not output any message in such a case.
Added test case with no .apple_name section in the file to verify new functionality.
Made existing test case more specific.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@305597 91177308-0d34-0410-b5e6-96231b3b80d8