pkgs/top-level/stage: refactor moving more generic package sets to the bottom

No change, just move appendOverlays and extend to the bottom, since they
will be changed much less often. This makes it easier to compare the
other package sets side-by-side.

pkgs/top-level/stage.nix

@@ -298,23 +298,6 @@ let
         localSystem = lib.systems.elaborate "${stdenv.hostPlatform.parsed.cpu.name}-linux";
       };
 
-    # Extend the package set with zero or more overlays. This preserves
-    # preexisting overlays. Prefer to initialize with the right overlays
-    # in one go when calling Nixpkgs, for performance and simplicity.
-    appendOverlays = extraOverlays:
-      if extraOverlays == []
-      then self
-      else nixpkgsFun { overlays = args.overlays ++ extraOverlays; };
-
-    # NOTE: each call to extend causes a full nixpkgs rebuild, adding ~130MB
-    #       of allocations. DO NOT USE THIS IN NIXPKGS.
-    #
-    # Extend the package set with a single overlay. This preserves
-    # preexisting overlays. Prefer to initialize with the right overlays
-    # in one go when calling Nixpkgs, for performance and simplicity.
-    # Prefer appendOverlays if used repeatedly.
-    extend = f: self.appendOverlays [f];
-
     # Fully static packages.
     # Currently uses Musl on Linux (couldn’t get static glibc to work).
     pkgsStatic = nixpkgsFun ({
@@ -357,6 +340,23 @@ let
         })
       ] ++ overlays;
     };
+
+    # Extend the package set with zero or more overlays. This preserves
+    # preexisting overlays. Prefer to initialize with the right overlays
+    # in one go when calling Nixpkgs, for performance and simplicity.
+    appendOverlays = extraOverlays:
+      if extraOverlays == []
+      then self
+      else nixpkgsFun { overlays = args.overlays ++ extraOverlays; };
+
+    # NOTE: each call to extend causes a full nixpkgs rebuild, adding ~130MB
+    #       of allocations. DO NOT USE THIS IN NIXPKGS.
+    #
+    # Extend the package set with a single overlay. This preserves
+    # preexisting overlays. Prefer to initialize with the right overlays
+    # in one go when calling Nixpkgs, for performance and simplicity.
+    # Prefer appendOverlays if used repeatedly.
+    extend = f: self.appendOverlays [f];
   };
 
   # The complete chain of package set builders, applied from top to bottom.