src: allow inspector without v8 platform

Embedders sometimes want to take control of V8 platform initialization
themselves, so we wouldn't want to experience an error if
NODE_USE_V8_PLATFORM was false necessarily. Instead, we can also gate
it with HAVE_INSPECTOR to allow embedders to define that themselves
and use Inspector without NODE_USE_V8_PLATFORM.

PR-URL: #30049
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Minwoo Jung <nodecorelab@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>
Reviewed-By: David Carlier <devnexen@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>

src/node_options.cc

@@ -27,10 +27,10 @@ std::shared_ptr<PerProcessOptions> cli_options{new PerProcessOptions()};
 }  // namespace per_process
 
 void DebugOptions::CheckOptions(std::vector<std::string>* errors) {
-#if !NODE_USE_V8_PLATFORM
+#if !NODE_USE_V8_PLATFORM && !HAVE_INSPECTOR
   if (inspector_enabled) {
     errors->push_back("Inspector is not available when Node is compiled "
-                      "--without-v8-platform");
+                      "--without-v8-platform and --without-inspector.");
   }
 #endif