getopt32: move support for "always treat first arg as option" to users (tar/ar)

getopt32: move support for "always treat first arg as option" to users (tar/ar)

Now getopt() never leaks (and never performs) any xmalloc's.

function                                             old     new   delta
ar_main                                              522     556     +34
tar_main                                             986    1014     +28
getopt32                                            1458    1350    -108
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(add/remove: 0/0 grow/shrink: 2/1 up/down: 62/-108)           Total: -46 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>