busybox

uname: make OS name configurable

A mailing list thread in September 2013 discussed changing the string
returned by the non-POSIX 'uname -o' option.  Nothing ever came of this
because there was no agreement as to what the string should be.

Make the string configurable so that people can decide for themselves.

Signed-off-by: Ron Yorston <rmy@frippery.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>