[ms-abi] Handle __declspec(align) on bitfields "properly"

__declspec(align), when applied to bitfields affects their perferred 
alignment instead of their required alignment.  We don't know why.  
Also, #pragma pack(n) turns packing *off* if n is greater than the 
pointer size.  This is now observable because of the impact of 
declspec(align) on bitfields.



git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198907 91177308-0d34-0410-b5e6-96231b3b80d8