loader: return empty globalPreload when not using off-thread loader

esm.mjs

@@ -1,13 +1,18 @@
 import { fileURLToPath } from 'url';
 import { createRequire } from 'module';
+import { versionGteLt } from './dist/util.js';
 const require = createRequire(fileURLToPath(import.meta.url));
 
 /** @type {import('./dist/esm')} */
 const esm = require('./dist/esm');
 export const { resolve, load, getFormat, transformSource } = esm.registerAndCreateEsmHooks();
 
 // Affordance for node 20, where load() happens in an isolated thread
+const offThreadLoader = versionGteLt(process.versions.node, '20.0.0');
 export const globalPreload = () => {
+  if (!offThreadLoader) {
+    return '';
+  }
   const self = fileURLToPath(import.meta.url);
   return `
 const { createRequire } = getBuiltin('module');