After much contemplation, I've decided that we probably shouldn't "unique"

__block object copy/dispose helpers for C++ objects with those for
different variables with completely different semantics simply because
they happen to both be no more aligned than a pointer.

Found by inspection.

Also, internalize most of the helper generation logic within CGBlocks.cpp,
and refactor it to fit my peculiar aesthetic sense.

llvm-svn: 128618