This is a follow-up for D62809.
Content and Size fields should be optional as was discussed in comments
of the D62809's thread. With that, we can describe a specific string table and
symbol table sections in a more correct way and also show appropriate errors.
The patch adds lots of test cases where the behavior is described in details.
Differential revision: https://reviews.llvm.org/D62957
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@362931 91177308-0d34-0410-b5e6-96231b3b80d8