Merge staging into closure-size

The most complex problems were from dealing with switches reverted in
the meantime (gcc5, gmp6, ncurses6).
It's likely that darwin is (still) broken nontrivially.

pkgs/development/libraries/libidn/default.nix

@@ -1,4 +1,4 @@
-{ fetchurl, stdenv }:
+{ fetchurl, stdenv, libiconv }:
 
 stdenv.mkDerivation rec {
   name = "libidn-1.32";
@@ -12,6 +12,8 @@ stdenv.mkDerivation rec {
 
   doCheck = ! stdenv.isDarwin;
 
+  buildInputs = stdenv.lib.optional stdenv.isDarwin libiconv;
+
   meta = {
     homepage = http://www.gnu.org/software/libidn/;
     description = "Library for internationalized domain names";