liquidwar: fix build (#125480)

Co-authored-by: Sandro <[e-mail]>

pkgs/games/liquidwar/default.nix

···
 , expat, gettext, perl, guile
 , SDL, SDL_image, SDL_mixer, SDL_ttf
 , curl, sqlite, libtool, readline
-, libogg, libvorbis, libcaca, csound, cunit } :
+, libogg, libvorbis, libcaca, csound, cunit
+, pkg-config }:
 
 stdenv.mkDerivation rec {
   pname = "liquidwar6";
···
     libXrender libcaca cunit
     libtool readline
   ];
+
+  nativeBuildInputs = [ pkg-config ];
 
   hardeningDisable = [ "format" ];