This commit updates the test output for the updated NLL compare mode
that uses `-Z borrowck=migrate` rather than `-Z borrowck=mir`. The
previous commit changes `compiletest` and this commit only updates
`.nll.stderr` files.
Give a special message when the later use is from a call. Use the span
of the callee instead of the whole expression. For conflicting borrow
messages say that the later use is of the first borrow.
