The build was failing due to missing telepathy_logger dependency,
I added it. Additionally, the connection to server was failing due to
telepathy executables not having an access to dconf, which was fixed
in #26113. Lastly, when I tried running Polari directly, it terminated
with SIGTRAP and the following error:
(org.gnome.Polari:22998): GLib-GIO-ERROR **: Settings schema 'org.gnome.desktop.interface' is not installed
adding `gnome3.gsettings_desktop_schemas` as a buildInput fixed that.
requiredSystemFeatures is not a meta attribute but a derivation
attribute. So "big-parallel" was being ignored on e.g. chromium,
causing it to be built (and timing out) on slow machines.
http://hydra.nixos.org/build/45819778#tabs-buildsteps