Revert r215331, "unique_ptrify CompilerInstance::OutputFile(s) and remove a unique_ptr around a non-owning raw_ostream in CodeGenAction::CreateASTConsumer"

It cannot be compiled on Visual Studio 2012.

  clang\include\clang/Frontend/CompilerInstance.h(153):
error C2248: 'std::unique_ptr<_Ty>::unique_ptr' : cannot access private member declared in class 'std::unique_ptr<_Ty>'
            with
            [
                _Ty=llvm::raw_ostream
            ]
            D:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\memory(1447) : see declaration of 'std::unique_ptr<_Ty>::unique_ptr'
            with
            [
                _Ty=llvm::raw_ostream
            ]
            This diagnostic occurred in the compiler generated function 'clang::CompilerInstance::OutputFile::OutputFile(const clang::CompilerInstance::OutputFile &)'