luaformatter: fix darwin build

pkgs/development/tools/luaformatter/default.nix

@@ -27,6 +27,7 @@ stdenv.mkDerivation rec {
     description = "Code formatter for Lua";
     homepage = "https://github.com/Koihik/LuaFormatter";
     license = licenses.asl20;
+    platforms = platforms.all;
     maintainers = with maintainers; [ figsoda SuperSandro2000 ];
     mainProgram = "lua-format";
   };

pkgs/top-level/all-packages.nix

@@ -14178,7 +14178,7 @@ with pkgs;
 
   luaformatter = callPackage ../development/tools/luaformatter
     (lib.optionalAttrs stdenv.isDarwin {
-      stdenv = overrideCC stdenv llvmPackages_latest.clang;
+      stdenv = overrideCC stdenv llvmPackages_9.clang;
     });
 
   malt = callPackage ../development/tools/profiling/malt {};