[ms-abi] Reordering __declspec(align) pragma pack handling

This patch moves the check for pragma pack until after the application 
of __declspec align to before pragma pack.  This causes observable 
changes in the use of tail padding for bases.  A test case is included.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@199154 91177308-0d34-0410-b5e6-96231b3b80d8