cargo-about: fix darwin build

pkgs/tools/package-management/cargo-about/default.nix

@@ -1,4 +1,4 @@
-{ lib, rustPlatform, fetchFromGitHub }:
+{ lib, rustPlatform, fetchFromGitHub, stdenv, libiconv }:
 rustPlatform.buildRustPackage rec {
   pname = "cargo-about";
   version = "0.3.0";
@@ -12,6 +12,8 @@ rustPlatform.buildRustPackage rec {
 
   cargoSha256 = "sha256-NdzgIB6uXMtGiLwOACEIeAb4iv7mYLnwRte3M/TkSMA=";
 
+  buildInputs = lib.optional stdenv.isDarwin libiconv;
+
   meta = with lib; {
     description = "Cargo plugin to generate list of all licenses for a crate";
     homepage = "https://github.com/EmbarkStudios/cargo-about";