We lost copy semantics in r263730, because it only worked for a few very
specific cases. Move semantics don't have this issue. Sadly the
implementation is a bit messy but I don't know how to clean it up
without losing support for msvc 2013 :/

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@263785 91177308-0d34-0410-b5e6-96231b3b80d8