Bounty for GDM

[coypu%sdf.org@localhost]

Hi,

I'd like us to eventually have GNOME 3 packaged, preferably the latest
version.
GDM seems to be a somewhat standalone part of it: it can be used used
for starting non-GNOME3, and is also the "most patched" part of it.

I'd like to offer a bounty of $500 to whoever completes the bounty, with
the following condition.

Acceptance criteria:
- GDM from GNOME 3.36.x package builds
- GDM can start something like MATE on NetBSD
- Simple explanation on how to use GDM to start MATE (or another DE)
- If the contributor doing the bounty has pkgsrc commit access, it is
  committed to pkgsrc.

Offer valid until August 2020.

Note that GDM 3.36 is also the version available by OpenBSD ports and
their patches are likely useful.

The bounty is high to account to how it'll require updating
dependencies.