Currently it appears that library flags like -lidn can only be passed on the command line of ghci, but it would be convenient (and more consistent) to be have to have them able to work from the .ghci file. Attempts to do so are silently ignored in both 6.4.2 and 6.6.

The only other place it would make sense to pass it would be as something like OPTIONS_GHC, but that results in "unknown flags in # OPTIONS # pragma: -lidn" in 6.4.2 and appears to be silently ignored in 6.6.