astc-encoder: limit to 64-bit target architectures

Mark this package as supported only on 64 bit architectures, as the build fails for 32 bit targets. Maybe this can be fixed in the future

pkgs/tools/graphics/astc-encoder/default.nix

@@ -73,5 +73,6 @@ gccStdenv.mkDerivation rec {
     platforms = platforms.unix;
     license = licenses.asl20;
     maintainers = with maintainers; [ dasisdormax ];
+    broken = !gccStdenv.is64bit;
   };
 }