[dwarfdump] Verify line table prologue

This patch adds prologue verification, which is already present in
Apple's dwarfdump. It checks for invalid directory indices and warns
about duplicate file paths.

Differential revision: https://reviews.llvm.org/D37511

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312782 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed