to be a bit more sensible. The public interface now is first followed by
the implementation details.
This also resolves a FIXME to make something private -- it was already
possible as the one special caller was already a friend.
No functionality changed.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196095 91177308-0d34-0410-b5e6-96231b3b80d8