More fixes to get good error messages for bad archives.

Fixed the last incorrect uses of llvm_unreachable() in the code
which were actually just cases of errors in the input Archives.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277540 91177308-0d34-0410-b5e6-96231b3b80d8
11 files changed