iconv: remove usage on Linux in several packages

This fixes builds after #4419. Thanks to @vbgl for the original commit;
I changed that as I'm not sure whether passing null values to buildInputs is clean.

CC maintainers: @coroa, @peti, @phreedom, @robberer, @jcumming.

pkgs/applications/misc/gammu/default.nix

···
 { stdenv, fetchurl, python, pkgconfig, cmake, bluez, libusb1, curl
-, libiconv, gettext, sqlite }:
+, libiconvOrEmpty, gettext, sqlite }:
 
 with stdenv.lib;
 
···
 
   patches = [ ./bashcomp-dir.patch ];
 
-  buildInputs = [ python pkgconfig cmake bluez libusb1 curl libiconv
-    gettext sqlite ];
+  buildInputs = [ python pkgconfig cmake bluez libusb1 curl gettext sqlite ]
+    ++ libiconvOrEmpty;
 
   enableParallelBuilding = true;
 

pkgs/applications/networking/p2p/twister/default.nix

···
 { stdenv, fetchurl, autoconf, automake, libtool, pkgconfig, python
-, boost, db, openssl, geoip, libiconv, miniupnpc
+, boost, db, openssl, geoip, libiconvOrEmpty, miniupnpc
 , srcOnly, fetchgit
 }:
 
···
 
   buildInputs = [
     autoconf automake libtool pkgconfig python
-    boost db openssl geoip libiconv miniupnpc
-  ];
+    boost db openssl geoip miniupnpc
+  ] ++ libiconvOrEmpty;
 
   postPatch = ''
     sed -i -e '/-htmldir/s|(default: [^)]*)|(default: ${twisterHTML})|' \

pkgs/applications/science/astronomy/stellarium/default.nix

···
-{ stdenv, fetchurl, cmake, freetype, libpng, mesa, gettext, openssl, qt4, perl, libiconv }:
+{ stdenv, fetchurl, cmake, freetype, libpng, mesa, gettext, openssl, qt4, perl
+, libiconvOrEmpty }:
 
 stdenv.mkDerivation rec {
   name = "stellarium-0.12.4";
···
     sha256 = "11367hv9niyz9v47lf31vjsqkgc8da0vy2nhiyxgmk1i49p1pbhg";
   };
 
-  buildInputs = [ cmake freetype libpng mesa gettext openssl qt4 perl libiconv ];
+  buildInputs = [ cmake freetype libpng mesa gettext openssl qt4 perl ]
+    ++ libiconvOrEmpty;
 
   enableParallelBuilding = true;
 

pkgs/development/ocaml-modules/ocaml-text/default.nix

···
-{stdenv, fetchurl, libiconv, ocaml, findlib, ncurses}:
+{stdenv, fetchurl, libiconvOrNull, ocaml, findlib, ncurses}:
 
 stdenv.mkDerivation {
   name = "ocaml-text-0.6";
···
     sha256 = "0j8gaak0ajnlmn8knvfygqwwzs7awjv5rfn5cbj6qxqbxhjd5m6g";
   };
 
-  buildInputs = [ocaml findlib libiconv ncurses];
+  buildInputs = [ocaml findlib ncurses]
+    ++ stdenv.lib.optional (libiconvOrNull != null) libiconvOrNull;
 
-  configurePhase = "iconv_prefix=${libiconv} ocaml setup.ml -configure";
+  configurePhase =
+    (stdenv.lib.optionalString (libiconvOrNull != null) "iconv_prefix=${libiconvOrNull} ")
+    + "ocaml setup.ml -configure";
 
   createFindlibDestdir = true;
 
···
   meta = {
     homepage = "http://ocaml-text.forge.ocamlcore.org/";
     description = "OCaml-Text is a library for dealing with ``text'', i.e. sequence of unicode characters, in a convenient way. ";
-    license = "BSD";
+    license = stdenv.lib.licenses.bsd3;
     platforms = ocaml.meta.platforms;
-    maintainers = [
-    ];
   };
 }

pkgs/tools/filesystems/netatalk/default.nix

···
-{ fetchurl, stdenv, pkgconfig, db, libgcrypt, avahi, libiconv, pam, openssl }:
+{ fetchurl, stdenv, pkgconfig, db, libgcrypt, avahi, libiconvOrEmpty, pam, openssl }:
 
 stdenv.mkDerivation rec {
   name = "netatalk-3.1.0";
···
     sha256 = "1d8dc8ysslkis4yl1xab1w9p0pz7a1kg0i6fds4wxsp4fhb6wqhq";
   };
 
-  buildInputs = [ pkgconfig db libgcrypt avahi libiconv pam openssl ];
+  buildInputs = [ pkgconfig db libgcrypt avahi pam openssl ] ++ libiconvOrEmpty;
 
   configureFlags = [
     "--with-bdb=${db}"

pkgs/tools/misc/mdbtools/git.nix

···
 { stdenv, fetchurl, fetchgit, glib, readline, bison, flex, pkgconfig,
-  libiconv, autoconf, automake, libtool, which, txt2man, gnome_doc_utils,
+  libiconvOrEmpty, autoconf, automake, libtool, which, txt2man, gnome_doc_utils,
   scrollkeeper}:
 
 stdenv.mkDerivation {
···
     name = "mdbtools-git-export";
   };
 
-  buildInputs = [glib readline bison flex pkgconfig libiconv autoconf automake
-    libtool which txt2man gnome_doc_utils scrollkeeper ];
+  buildInputs = [
+    glib readline bison flex pkgconfig autoconf automake
+    libtool which txt2man gnome_doc_utils scrollkeeper
+  ] ++ libiconvOrEmpty;
 
   preConfigure = ''
     sed -e 's@static \(GHashTable [*]mdb_backends;\)@\1@' -i src/libmdb/backend.c

pkgs/tools/security/clamav/default.nix

···
-{ stdenv, fetchurl, zlib, bzip2, libiconv, libxml2, openssl, ncurses, curl }:
+{ stdenv, fetchurl, zlib, bzip2, libiconvOrNull, libxml2, openssl, ncurses, curl }:
 stdenv.mkDerivation rec {
   name = "clamav-${version}";
   version = "0.98.4";
···
     sha256 = "071yzamalj3rf7kl2jvc35ipnk1imdkq5ylbb8whyxfgmd3nf06k";
   };
 
-  buildInputs = [ zlib bzip2 libiconv libxml2 openssl ncurses curl ];
+  buildInputs = [ zlib bzip2 libxml2 openssl ncurses curl ]
+    ++ stdenv.lib.optional (libiconvOrNull != null) libiconvOrNull;
 
   configureFlags = [
     "--with-zlib=${zlib}"
     "--with-libbz2-prefix=${bzip2}"
-    "--with-iconv-dir=${libiconv}"
+  ] ++ (stdenv.lib.optional (libiconvOrNull != null)
+       "--with-iconv-dir=${libiconvOrNull}")
+  ++ [
     "--with-xml=${libxml2}"
     "--with-openssl=${openssl}"
     "--with-libncurses-prefix=${ncurses}"