[cmpcodesize] Use argparse
[cmpcodesize] Use argparse

Rather than manually parse the arguments passed to cmpcodesize, use the
Python stdlib. By doing so, we can eliminate a lot of redundant code.

One problem: argparse can't handle positional arguments of the string
'--', since it misinterprets them as optional arguments. We replace
that stirng with a special token.

khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift,khizkhiz/swift