Fixing PR18510 by checking whether the non-virtual base of the derived class

might have a smaller size as compared to the stand-alone type of the base class.
This is possible when the derived class is packed and hence might have smaller
alignment requirement than the base class.

Differential Revision: http://llvm-reviews.chandlerc.com/D2599



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200031 91177308-0d34-0410-b5e6-96231b3b80d8