The `settings-docs.c` file is generated by processing the
`nm-property-docs.xml` file. Although this works in autotools,
the `.c` extension makes meson not to handle it properly.
Given the fact that it only contains a number of defines it
makes sense to change its extension to `.h` an use it as a header.
This also makes meson to handle it properly and build it before
its used.
https://mail.gnome.org/archives/networkmanager-list/2018-January/msg00057.html
Even Gentoo disables this plugin since before 0.9.8 release
of NetworkManager. Time to say goodbye.
If somebody happens to show up to maintain it, we may resurrect it
later.
If "$distro_plugins=ifnet" was set, configure.ac would use that
to autodetect --with-hostname-persist=gentoo. Replace that autodetect
part by checking for /etc/gentoo-release file.
Since meson 0.44 there is a new option type called `array`, which
allows to use an array with different values in those options.
These fits the needs of different options that are used to pass
binary paths, which have multiple paths as an alternate locations.
meson's version has been bumped to 0.44 and different options have
been changed to `array` type options.
https://mail.gnome.org/archives/networkmanager-list/2017-December/msg00062.html
