libnids: fix cross build

pkgs/by-name/li/libnids/package.nix

···
     url = "mirror://sourceforge/libnids/libnids-1.24.tar.gz";
     sha256 = "1cblklfdfxcmy0an6xyyzx4l877xdawhjd28daqfsvrh81mb07k1";
   };
+
+  postPatch = ''
+    substituteInPlace src/Makefile.in \
+      --replace-fail ar '${stdenv.cc.targetPrefix}ar'
+  '';
+
   nativeBuildInputs = [ pkg-config ];
   buildInputs = [
     libpcap