libnatspec: unmark broken on darwin

pkgs/development/libraries/libnatspec/default.nix

···
   propagatedBuildInputs = [ libiconv ];
 
   meta = with lib; {
-    broken = stdenv.isDarwin;
     homepage = "http://natspec.sourceforge.net/";
     description = "A library intended to smooth national specificities in using of programs";
     platforms = platforms.unix;