I see `--enable-nls` option in `./configure --help`.
So let's add `nls` flag support?
Well, `--with-libnm-glib` option, also (`glib` flag).
Also, I see
in a neighbor https://gitweb.gentoo.org/repo/gentoo.git/tree/net-vpn/networkmanager-libreswan/networkmanager-libreswan-1.2.12.ebuild which are acceptable by networkmanager-l2tp's `./configure`.
Providing an option for nls makes no sense.
Some of the rest seem relevant, especially explicitly forcing off libnm-glib with --without-libnm-glib feels appropriate to ensure things are good with the p.masked networkmanager
I'm pretty certain `--with-dist-version=Gentoo` is incorrect and not a good idea, here are some examples from other Linux distribution for NetworkManager-l2tp-1.8.6 :
Fedora 35 :
Ubuntu 20.04 :
So basically `--with-dist-version` is intended to have the software version number and the linux distribution's revision number of the package.
I vaguely remember `--disable-more-warnings` was required a long time ago to successfully build the NetworkManager VPN clients on 32bit platforms when used in combination with -Werror, but that issue was fixed ages ago.
Regarding `--with-libnm-glib` / `--without-libnm-glib`, extract from the NEWS file for NetworkManager 1.20 :
* The libnm-glib library, deprecated in favor of libnm since
NetworkManager 1.0, and disabled by default since NetworkManager 1.12, has now been removed.
The majority of VPN clients now have `--without-libnm-glib` as their default.
libnm-glib code will most likely eventually get removed from the VPN clients.
Explicitly using `--without-libnm-glib` might make some sense, but `--with-libnm-glib` definitely doesn't.