Fix the field count in interface record layout (it was incorrectly

Fix the field count in interface record layout (it was incorrectly
compensating for super classes). This was making the reported class
sizes for empty classes very, very wrong.
 - Also, we now report the size info for an empty class like gcc (as
   the offset of the start, not as 0, 0).

 - Add a few more test cases we were mishandling before (padding bit
   field at end of struct, for example).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@70938 91177308-0d34-0410-b5e6-96231b3b80d8