src/optparse.lisp: Rearrange system-specific stuff.

src/optparse.lisp: Rearrange system-specific stuff.

  * Remove `cl-launch' from the explicit `:use' list.

  * Prefer using `uiop' to collect arguments if it's present, because it
    does everything properly.

  * Fall back to `cl-launch' driven by steam if it's available.

  * Otherwise use a hacky list of system-specific runes copied from my
    other Lisp library.

  * Reformat the `exit' function so it's easier to slot new
    implementations in, similar to the new `set-command-line-arguments'.

  * Load `sod-frontend' and use `optparse:exit' rather than
    `cl-launch:quit', because the latter has disappeared in later
    versions.