php.buildEnv: Put the extraConfig snippet after extensions

Make sure all the extensions are loaded first, then read the custom
config where possible.

pkgs/development/interpreters/php/default.nix

@@ -178,9 +178,9 @@ let
 
           extNames = map getExtName extList;
           extraInit = writeText "custom-php.ini" ''
-            ${extraConfig}
             ${lib.concatStringsSep "\n"
               (lib.textClosureList extensionTexts extNames)}
+            ${extraConfig}
           '';
         in
           symlinkJoin {