$PATH contains directories twice

Since f440e2db the $PATH on my machine, as set by /etc/profile, contains many common directory twice. Presently, the default $PATH created by a /bin/sh login shell (i.e. ash) looks as follows:

$ env -i sh -l
$ echo $PATH
/sbin:/usr/sbin:/bin:/usr/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

As one can see /sbin, /usr/sbin, /bin, and /usr/bin are contained twice in $PATH. This is due to the fact that busybox ash sets $PATH to /sbin:/usr/sbin:/bin:/usr/bin before sourcing /etc/profile. Since commit f440e2db /etc/profile then appends to $PATH causing the entries already included by ash itself to be listed twice in $PATH. This seems weird and is also undesirable since these directories will be searched twice by execl, execv, execle, et cetera.

If we really need to append to $PATH one solution would be checking if a given directory is already part of $PATH before appending it to $PATH. This is what Arch Linux does for instance https://github.com/archlinux/svntogit-packages/blob/ed2da51a91162eaa0916dc3d9725fb2b574fb901/trunk/profile#L6-L20