linux-user, bsd-user: Preserve incoming order of environment variables in the target

Do not reverse the order of environment variables in the target environ
array relative to the incoming environ order.  Some testsuites depend on a
specific order, even though it is not defined by any standard.

Signed-off-by: Andreas Schwab <schwab@suse.de>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <mvmlejfsivd.fsf@suse.de>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>