This change moves LTOCodeGenerator's ownership of the merged module to a
field of type std::unique_ptr<Module>. This helps simplify parts of the code
and clears the way for the module to be consumed by LLVM CodeGen (see D12132
review comments).
Differential Revision: http://reviews.llvm.org/D12205
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@245891 91177308-0d34-0410-b5e6-96231b3b80d8