[MS-ABI] Update virtual base padding rules to match MSVC 10+

In version 9 (VS2010) (and prior)? versions of msvc, if the last field 
in a record was a bitfield padding equal to the size of the storage 
class of that bitfield was added before each vbase and vtordisp.  This 
patch removes that feature from clang and updates the lit tests to 
reflect it. 

llvm-svn: 206004