[C++11] Add overloads for externally used OwningPtr functions.

This will allow external callers of these functions to switch over time
rather than forcing a breaking change all a once. These particular
functions were determined by building clang/lld/lldb.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@202959 91177308-0d34-0410-b5e6-96231b3b80d8