Introduce config.me.optimizations.enable to toggle optimizations.

This is more granular than the buildingIso setting.

nix/configuration/roles/global_options/default.nix

@@ -9,7 +9,12 @@
   imports = [ ];
 
   options.me = {
-
+    optimizations.enable = lib.mkOption {
+      type = lib.types.bool;
+      default = false;
+      example = true;
+      description = "Whether we want to enable CPU optimizations (will trigger a rebuild from source).";
+    };
   };
 
   # options.me.graphics_card_type = lib.mkOption {