libnatspec: The build process doesn't respect buildInputs, so force use of libiconv on not-Linux

pkgs/development/libraries/libnatspec/default.nix

@@ -1,6 +1,6 @@
-{ stdenv, fetchurl, popt, libiconvOrEmpty }:
+{ stdenv, fetchurl, popt, libiconv }:
 
-stdenv.mkDerivation rec {
+stdenv.mkDerivation (rec {
   name = "libnatspec-0.2.6";
 
   src = fetchurl {
@@ -8,7 +8,7 @@ stdenv.mkDerivation rec {
     sha256 = "0zvm9afh1skxgdv62ylrpwyykpjhhskxj0zv7yrdf7jhfdriz0y3";
   };
 
-  buildInputs = [ popt ] ++ libiconvOrEmpty;
+  buildInputs = [ popt ];
 
   meta = {
     homepage = http://natspec.sourceforge.net/ ;
@@ -16,4 +16,8 @@ stdenv.mkDerivation rec {
     platforms = stdenv.lib.platforms.unix;
     maintainers = [ stdenv.lib.maintainers.urkud ];
   };
-}
+} // stdenv.lib.optionalAttrs (!stdenv.isLinux) {
+  NIX_CFLAGS_COMPILE = "-I${libiconv}/include";
+
+  NIX_CFLAGS_LINK = "-L${libiconv}/lib -liconv";
+})