Builds the text renderer for this computer and checks the fonts, so an app
can run here with config :nest_gen2, target: :host (see docs/host.md).
mix nest_gen2.hostNeeds a C compiler (cc). The renderer goes to ~/.nest_gen2_sdk/bin. The
fonts are Nest's own and aren't shipped with the SDK: copy them from your
Nest to ~/.nest_gen2_sdk/fonts as docs/host.md shows.