ash: align --login code with dash

ash: align --login code with dash

Upstream commit:

    Date: Sun, 13 Jul 2008 22:34:50 +0800
    [OPTIONS] Added support for -l

    This patch adds support for the -l option (login shell) as required
    by the LSB.

    Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
It's a bit bigger, but gets rid of one global variable

function                                             old     new   delta
options                                              554     576     +22

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