Move to llvm-readobj code that is only used there.

lld might end up using a small part of this, but it will be in a much
refactored form. For now this unblocks avoiding the full section scan in the
ELFFile constructor.

This also has a (very small) error handling improvement.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244282 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed