Fix nix mac issues building core missing newer apple sdk libs (#12746)

flake.nix

@@ -10,9 +10,14 @@
     flake-utils.lib.eachDefaultSystem (system:
       let
         pkgs = import nixpkgs { inherit system; overlays = [ ]; };
+        # The current default sdk for macOS fails to compile go projects, so we use a newer one for now.
+        # This has no effect on other platforms.
+        callPackage = pkgs.darwin.apple_sdk_11_0.callPackage or pkgs.callPackage;
       in
       rec {
-        devShell = pkgs.callPackage ./shell.nix { };
+        devShell = callPackage ./shell.nix {
+          inherit pkgs;
+        };
         formatter = pkgs.nixpkgs-fmt;
       });
 }

nix.conf

@@ -0,0 +1 @@
+experimental-features = nix-command flakes

shell.nix

@@ -1,4 +1,4 @@
-{ pkgs ? import <nixpkgs> { } }:
+{ pkgs }:
 with pkgs;
 let
   go = go_1_21;
@@ -46,6 +46,7 @@ mkShell {
   ];
   LD_LIBRARY_PATH = "${stdenv.cc.cc.lib}/lib64:$LD_LIBRARY_PATH";
   GOROOT = "${go}/share/go";
+  CGO_ENABLED = 0;
 
   PGDATA = "db";
   CL_DATABASE_URL = "postgresql://chainlink:chainlink@localhost:5432/chainlink_test?sslmode=disable";