openclonk: fix build

cmake complained about not finding X11_LIBRARIES, which is fixed by
providing libXrandr.

Adding ninja fixes the installPhase which fails randomly. There is a
hack in upstream's CMakeLists.txt file that reads:

  USES_TERMINAL # Hack: prevent parallel execution (for ninja), c4group
tends to fail otherwise

This only works with ninja, though. Also enable parallel install phase
again, since this seems to work with ninja now.

This also fixes the build for aarch64-linux.

pkgs/by-name/op/openclonk/package.nix

@@ -9,6 +9,7 @@
 
   # nativeBuildInputs
   cmake,
+  ninja,
   pkg-config,
 
   gcc-unwrapped,
@@ -24,6 +25,7 @@
   libogg,
   libpng,
   libvorbis,
+  libXrandr,
   openal,
   readline,
   SDL2,
@@ -60,14 +62,13 @@ stdenv.mkDerivation {
     })
   ];
 
-  enableParallelInstalling = false;
-
   postInstall = lib.optionalString enableSoundtrack ''
     ln -sv ${soundtrack_src} $out/share/games/openclonk/Music.ocg
   '';
 
   nativeBuildInputs = [
     cmake
+    ninja
     pkg-config
   ];
 
@@ -82,6 +83,7 @@ stdenv.mkDerivation {
     libogg
     libpng
     libvorbis
+    libXrandr
     openal
     readline
     SDL2
@@ -101,9 +103,6 @@ stdenv.mkDerivation {
     license = if enableSoundtrack then licenses.unfreeRedistributable else licenses.isc;
     mainProgram = "openclonk";
     maintainers = [ ];
-    platforms = [
-      "x86_64-linux"
-      "i686-linux"
-    ];
+    platforms = lib.platforms.linux;
   };
 }