[DWARF] Modification of code for the verification of .debug_info section.

[DWARF] Modification of code for the verification of .debug_info section.

Summary:
This patch modifies the handleDebugInfo() function so that we verify the contents of each unit
in the .debug_info section only if its header has been successfully verified.

This change will allow for more/different verification checks depending on the type of the unit since from
dwarf5, the .debug_info section may consist of different types of units.

Subscribers: aprantl

Differential Revision: https://reviews.llvm.org/D35521

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@308245 91177308-0d34-0410-b5e6-96231b3b80d8