[LCG] Make the iterator move constructable (and thus movable in general)
now that there is essentially no cost to doing so. Yay C++11.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203447 91177308-0d34-0410-b5e6-96231b3b80d8
[LCG] Make this call graph a fully regular type by giving it assignment
as well. I don't see any particular need but it imposes no cost to
support it and it makes the API cleaner.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203448 91177308-0d34-0410-b5e6-96231b3b80d8