env: Fix compatibility with glibc getopt

[wezm]

Fixes:

$ echo asdf | src.freebsd/coreutils/env/env FOO=bar sed -n 's/asdf/qwer/'
src.freebsd/coreutils/env/env: invalid option -- 'n'
usage: env [-0iv] [-C workdir] [-L|-U user[/class]] [-P utilpath] [-S string]
           [-u name] [name=value ...] [utility [argument ...]]