src: fix build break for !NODE_USE_V8_PLATFORM

`StartInspector` should return `bool` but there was signature
mismatch if not building for v8 platform i.e.
`!NODE_USE_V8_PLATFORM`

PR-URL: https://github.com/nodejs/node/pull/8114
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>

src/node.cc

@@ -220,8 +220,9 @@ static struct {
   void Initialize(int thread_pool_size) {}
   void PumpMessageLoop(Isolate* isolate) {}
   void Dispose() {}
-  void StartInspector(Environment *env, int port, bool wait) {
+  bool StartInspector(Environment *env, int port, bool wait) {
     env->ThrowError("Node compiled with NODE_USE_V8_PLATFORM=0");
+    return false;  // make compiler happy
   }
 #endif  // !NODE_USE_V8_PLATFORM
 } v8_platform;