Clean up arc annotations by moving the top/bottom BB annotations into conditional macros that no-op in Release mode instead of #ifdef sections of the code.

This is to follow the example of the DEBUG macro.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178705 91177308-0d34-0410-b5e6-96231b3b80d8