nixFlakes: enable flakes,nix-command via patch

pkgs/tools/package-management/nix/default.nix

@@ -227,13 +227,8 @@ in rec {
     inherit storeDir stateDir confDir boehmgc;
   });
 
-  nixFlakes = callPackage ({ makeWrapper, runCommand, ... }:
-    runCommand "nix-flakes" { buildInputs = [ makeWrapper ]; } ''
-      mkdir -p $out/bin
-        for bin in ${nixUnstable}/bin/*; do
-          makeWrapper $bin $out/bin/$(basename $bin) \
-            --suffix NIX_CONFIG "\n" "experimental-features = nix-command flakes"
-        done;
-    '') {};
+  nixFlakes = nixUnstable.overrideAttrs (prev: {
+    patches = (prev.patches or []) ++ [ ./enable-flakes.patch ];
+  });
 
 }

pkgs/tools/package-management/nix/enable-flakes.patch

@@ -0,0 +1,14 @@
+diff --git a/src/libstore/globals.hh b/src/libstore/globals.hh
+index 3e4ead76c..81d407236 100644
+--- a/src/libstore/globals.hh
++++ b/src/libstore/globals.hh
+@@ -923,7 +923,8 @@ public:
+           value.
+           )"};
+ 
+-    Setting<Strings> experimentalFeatures{this, {}, "experimental-features",
++    Setting<Strings> experimentalFeatures{
++        this, {"flakes", "nix-command"}, "experimental-features",
+         "Experimental Nix features to enable."};
+ 
+     bool isExperimentalFeatureEnabled(const std::string & name);