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

[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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206004 91177308-0d34-0410-b5e6-96231b3b80d8