[analyzer] Invalidate destination of std::copy() and std::copy_backward().

Now that the libcpp implementations of these methods has a branch that doesn't call
memmove(), the analyzer needs to invalidate the destination for these methods explicitly.

rdar://problem/23575656

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@260043 91177308-0d34-0410-b5e6-96231b3b80d8