teeworlds: add buildClient feature flag

Allows for only building the Teeworlds server (for example, in a
headless environment). This gets rid of a great deal of dependencies
which would be unneccessary in a headless server.

Also added the package "teeworlds-server" in all-packages.nix, defined
as an override.

pkgs/games/teeworlds/default.nix

···
 , nixosTests
 , Carbon
 , Cocoa
+, buildClient ? true
 }:
 
 stdenv.mkDerivation rec {
···
   nativeBuildInputs = [
     cmake
     pkg-config
-  ] ++ lib.optionals stdenv.isLinux [
+  ] ++ lib.optionals (buildClient && stdenv.isLinux) [
     icoutils
   ];
 
   buildInputs = [
-    python3 libGLU SDL2 lua5_3 zlib freetype wavpack
+    python3 lua5_3 zlib
+  ] ++ lib.optionals buildClient ([
+    libGLU
+    SDL2
+    freetype
+    wavpack
   ] ++ lib.optionals stdenv.isLinux [
     alsa-lib
     libX11
   ] ++ lib.optionals stdenv.isDarwin [
     Carbon
     Cocoa
+  ]);
+
+  cmakeFlags = [
+    "-DCLIENT=${if buildClient then "ON" else "OFF"}"
   ];
 
-  postInstall = lib.optionalString stdenv.isLinux ''
+  postInstall = lib.optionalString buildClient (lib.optionalString stdenv.isLinux ''
     # Convert and install desktop icon
     mkdir -p $out/share/pixmaps
     icotool --extract --index 1 --output $out/share/pixmaps/teeworlds.png $src/other/icons/teeworlds.ico
···
     cp '../other/bundle/client/PkgInfo' "$out/Applications/teeworlds.app/Contents/"
     ln -s "$out/bin/teeworlds" "$out/Applications/teeworlds.app/Contents/MacOS/"
     ln -s "$out/share/teeworlds/data" "$out/Applications/teeworlds.app/Contents/Resources/data"
-  '';
+  '');
 
   passthru.tests.teeworlds = nixosTests.teeworlds;
 

pkgs/top-level/all-packages.nix

···
   teeworlds = callPackage ../games/teeworlds {
     inherit (darwin.apple_sdk.frameworks) Carbon Cocoa;
   };
+  teeworlds-server = teeworlds.override { buildClient = false; };
 
   tengine = callPackage ../servers/http/tengine {
     modules = with nginxModules; [ rtmp dav moreheaders modsecurity ];