I am not sure why this occurs either, it only appears that after the
assignment, `old_loop_target` and `loop_target` are both referencing the
same variable, causing the next line to set both variables as None.
All parameters with a structure type in extern functions are marked as
`byref` instead of `byval`, as most ABIs require the first several
arguments to be passed in registers before spilling into the stack.
`byval` breaks this contract by explicitly requiring all arguments to be
passed in the stack, breaking interop with libraries written in other
languages.