Replace uses of the deprecated std::auto_ptr with OwningPtr.

This is a rework of the broken parts in r179373 which were subsequently reverted in r179374 due to incompatibility with C++98 compilers.  This version should be ok under C++98.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179520 91177308-0d34-0410-b5e6-96231b3b80d8