Remove some calls to std::move.

Instead of moving out the data in a ErrorOr<std::unique_ptr<Foo>>, get
a reference to it.

Thanks to David Blaikie for the suggestion.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@214516 91177308-0d34-0410-b5e6-96231b3b80d8