fix(ssr): avoid hard-coded ssr checks in cjs builds

packages/runtime-core/src/apiWatch.ts

@@ -21,7 +21,8 @@ import {
   currentInstance,
   ComponentInternalInstance,
   currentSuspense,
-  Data
+  Data,
+  isInSSRComponentSetup
 } from './component'
 import {
   ErrorCodes,
@@ -86,8 +87,8 @@ export function watch<T = any>(
   cbOrOptions?: WatchCallback<T> | WatchOptions,
   options?: WatchOptions
 ): StopHandle {
-  if (__SSR__ && !(options && options.flush === 'sync')) {
-    // during SSR, non-sync watchers never fire.
+  if (isInSSRComponentSetup && !(options && options.flush === 'sync')) {
+    // component watchers during SSR are no-op
     return NOOP
   } else if (isFunction(cbOrOptions)) {
     // effect callback as 2nd argument - this is a source watcher