swift234

[cmpcodesize] Use Python indices for separator

Because of the way Python uses references for lists, the logic around
`oldFileArgs`, `newFileArgs`, and `curFiles` is difficult to follow.
Use a less efficient algorithm to find and split the elements based on
the '--' separator.

Although its performance is negligibly worse O(2n) as opposed to O(n), it's
easier to understand and uses one less imperative loop. Also, it's not as if
we'll ever encounter input that makes the performance difference
matter, so :shipit:!