`sh -l` - PATH not exported

[Irae Hueck Costa]

When I invoke a login shell (sh -l), PATH is set but not exported. The behaviour with Fedora, Debian, Alpine, CentOS and I think I tested others is to export PATH in that case.

On my xenial and a (chrooted) bionic:
```
$ env -i sh -l
$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
$ printenv
PWD=/home/irae/plash
```

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

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[costi (iraehc)]

I am the same user that registered the bug (No idea which email I used)

[costi (iraehc)]

I assigned to `base-files` because I imagine it could be something with /etc/profile /etc/profile.d /etc/environment or so, but it is honestly a shot in the dark. I could not localize it.