SDL2_image: fix cross

pkgs/development/libraries/SDL2_image/default.nix

@@ -1,4 +1,7 @@
-{ lib, stdenv, fetchurl, SDL2, libpng, libjpeg, libtiff, giflib, libwebp, libXpm, zlib, Foundation }:
+{ lib, stdenv, fetchurl
+, pkg-config
+, SDL2, libpng, libjpeg, libtiff, giflib, libwebp, libXpm, zlib, Foundation
+}:
 
 stdenv.mkDerivation rec {
   pname = "SDL2_image";
@@ -9,6 +12,8 @@ stdenv.mkDerivation rec {
     sha256 = "1l0864kas9cwpp2d32yxl81g98lx40dhbdp03dz7sbv84vhgdmdx";
   };
 
+  nativeBuildInputs = [ pkg-config ];
+
   buildInputs = [ SDL2 libpng libjpeg libtiff giflib libwebp libXpm zlib ]
     ++ lib.optional stdenv.isDarwin Foundation;