[codeview] Check for a DIExpression offset for local variables

[codeview] Check for a DIExpression offset for local variables

Fixes inalloca parameters, which previously all pointed to the same
offset. Extend the test to use llvm-readobj so that we can test the
offset in a readable way.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@302578 91177308-0d34-0410-b5e6-96231b3b80d8