[MS-ABI] Update Comments in RecordLayoutBuilder - no functional change
This patch updates the comments in RecordLayoutBuilder about record 
layout in the MS-ABI.  Also, I added a section about known 
incompatibilities.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@206010 91177308-0d34-0410-b5e6-96231b3b80d8