Documentation should be installed.
We may want to pass LANG=en_US.UTF-8 as an environment variable.

I did see these warnings during compile for 1.3.2, but I think this is an Elixir problem not a pkgsrc one:

==> elixir (compile)
warning: behaviour String.Chars undefined
  lib/calendar.ex:292

warning: behaviour Inspect undefined
  lib/calendar.ex:298

warning: variable status is unused
  lib/enum.ex:864

warning: the Dict module is deprecated
  lib/hash_dict.ex:10

Compiling lib/calendar/iso.ex (it's taking more than 5s)
Compiling lib/file/stat.ex (it's taking more than 5s)
warning: behaviour String.Chars undefined
  lib/calendar.ex:556

Compiling lib/gen_event.ex (it's taking more than 5s)
warning: behaviour String.Chars undefined
  lib/calendar.ex:907

warning: behaviour String.Chars undefined
  lib/calendar.ex:1212
