[ms-abi] Refactor Microsoft Record Layout

This patch refactors microsoft record layout to be more "natural".  The 
most dominant change is that vbptrs and vfptrs are injected after the 
fact.  This simplifies the implementation and the math for the offest 
for the first base/field after the vbptr.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198818 91177308-0d34-0410-b5e6-96231b3b80d8