[llvm-readobj] Update readobj to re-use parsing code.

llvm-readobj hand rolls some CodeView parsing code for string
tables, so this patch updates it to re-use some of the newly
introduced parsing code in LLVMDebugInfoCodeView.

Differential Revision: https://reviews.llvm.org/D32772

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302052 91177308-0d34-0410-b5e6-96231b3b80d8
14 files changed