Xcrun output broken when completing a single dash

[PatTheMav]

Since #13 was merged, the output for xcrun is broken when a single dash is intended to be completed (i.e. xcrun -<tab> is typed in the terminal).

The output is broken in a similar way to how the completions for xcodebuild were broken before #16 was fixed (see also: #2 (comment)).

Once again the POSIX and GNU arguments are not grouped, with GNU arguments listed first, followed by the posix arguments with empty lines added for non-matching GNU arguments, followed by the description for each, before the pattern is repeated.

I haven't had time to dig into a fix for this, but my hunch is that either (or both) of these seem to trip up the system:

  '(-)1: :->executables' \
  '*:: : _normal' \

The completion system (at least under my Zsh config) will ask whether I want it to display all 97 lines, and when I accept the broken output as described above occurs and the cursor jumps before the dash.

Using double-dashes (to get completions for GNU-style arguments) does work, as well as providing no argument at all (available commands are listed) and as far as I can tell the SDK and toolchain completion behaviour is correct. So it's only the completion for POSIX-style arguments that is broken.