objective-C blocks: Make sure that identical logic is used

objective-C blocks: Make sure that identical logic is used
in deciding a copy/dispose field is needed in a byref structure
and when generating the copy/dispose helpers. In certain
cases, these fields were being added but no copy/dispose was
being generated. This was uncovered in ARC, but not in MRR.
// rdar://12759433

llvm-svn: 168825