PR12208: Under -fno-elide-constructors, don't forget to actually copy an NRVO
variable to the return slot. Patch by David Wiberg, with test case alterations
by me.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@198991 91177308-0d34-0410-b5e6-96231b3b80d8