Fix compile on lacros

The V8 roll is stuck due to a compile error:
https://chromium-review.googlesource.com/c/chromium/src/+/2933917

This CL adds the defined() to a preprocessor guard to make it
compile

Change-Id: I744c6b9c3b92380a80fd50393e86f48392042b9a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2939985
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74944}

src/d8/d8.cc

@@ -2803,13 +2803,13 @@ Local<ObjectTemplate> Shell::CreateGlobalTemplate(Isolate* isolate) {
 Local<ObjectTemplate> Shell::CreateOSTemplate(Isolate* isolate) {
   Local<ObjectTemplate> os_template = ObjectTemplate::New(isolate);
   AddOSMethods(isolate, os_template);
-#if V8_TARGET_OS_LINUX
+#if defined(V8_TARGET_OS_LINUX)
   const char os_name[] = "linux";
-#elif V8_TARGET_OS_WIN
+#elif defined(V8_TARGET_OS_WIN)
   const char os_name[] = "windows";
-#elif V8_TARGET_OS_MACOSX
+#elif defined(V8_TARGET_OS_MACOSX)
   const char os_name[] = "macos";
-#elif V8_TARGET_OS_ANDROID
+#elif defined(V8_TARGET_OS_ANDROID)
   const char os_name[] = "android";
 #else
   const char os_name[] = "unknown";