Try to appease the C++ gods

Looks like some builds were not happy with the potentially-throwing move
constructor that was added in r220723, and reached for the implicitly
deleted copy constructor instead.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@220725 91177308-0d34-0410-b5e6-96231b3b80d8