[Toybox] tar -I

[enh]

TIL that apparently gnu tar's -I can be something like "prog -a -b
-c", not just "prog".

(found by someone trying to modify the compression level of the
archiver they were using.)

is there any precedent for that with other commands? i don't know
whether gnu tar is calling system() or doing its own shell parsing,
but either sounds like a terrible idea. (-I should probably have been
a list of strings instead.)