Pass a && to getLazyBitcodeModule.

This forces callers to use std::move when calling it. It is somewhat odd to have
code with std::move that doesn't always move, but it is also odd to have code
without std::move that sometimes moves.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217049 91177308-0d34-0410-b5e6-96231b3b80d8