(verbose_usage): Remove function. Move contents into usage.

(verbose_usage): Remove function.  Move contents into usage.
Remove lots of #if directives involving FLASK_LINUX
[!FLASK_LINUX] (is_flask_enabled): Define.
(stat_secure, lstat_secure): Define.
(print_statfs): Remove lots of nested #if directives.
Instead, rely on support fo %llu and %lld printf formats --
but that is only temporary, since it's not porable enough.
(main): Hoist is_flask_enabled test to be done here, rather
than in each of do_stat and do_statfs for every argument.